Caramelized Onion and Arugula Tostadas

Crispy corn tortillas topped with melt-in-your-mouth onions, peppery arugula, and creamy avocado–these caramelized onion and arugula tostadas have it all!

  Click here to PIN Caramelized Onion and Arugula Tostadas.

Tostadas are basically open face tacos,  crispy edible plates with all the goodies on top instead of inside.

For these vegetarian tostadas, in addition to the avocado chunks, caramelized sweet onions and spicy arugula, I’ve added a sprinkle of white cheddar cheese, diced fresh tomatoes and a drizzle of tangy yogurt. Caramelized onion and arugula tostadas are also delicious without the cheese and yogurt. My vegan version gets a fat drizzle of creamy guacamole avocado lime sauce.

Our favorite way to eat tostadas is build-your-own. You toast the tortillas so they are ready and waiting, then set out bowls of the topping ingredients. At the table or on a buffet, people can layer the onions, shredded arugula, tomatoes, avocado, cilantro, salsa, lime wedges etc., choosing  more of what they want, skipping what they don’t.

Tips for how to caramelize onions:

• Slowly and gently. Caramelized onions don’t happen quickly. It takes minimum 45 minutes (and often over an hour) over low heat for the natural sugars in the onions to caramelize.
• When you slowly cook onions for an extended period, the onion’s natural sugars take on a rich umami, well, caramely flavor. Take care to cook the onions gently so as not to hurry their caramelization. If they start to brown too quickly, turn down the heat and put a lid on the pan.
• Placing a lid on the pan when you turn down the heat creates a little steam and speeds up the process. The steam also helps keep the onions from drying out.
• “Sweet” onion varietals like Walla-Walla and Vidalias caramelize well because of their higher percentage of natural sugar. that said, use whatever onions you have. Even red onions.
• It seems like a lot of onions at the start, but by the time they’ve caramelized you will wonder if you have enough to top your tostadas.
• To slice the onions, I used the medium slicing blade (4 mm) that came with my food processor. No tears.

If you can find diminutive (4-inch) round corn tortillas, “taco sliders”, use them. Mi Rancho taco sliders are my favorites. All crispy and crunchy, the slider-size tortillas are easier to manage in your hands (and mouth) than the regular 6-inch rounds. Plus you can eat several and feel good about it. Robbie gobbled up six in one sitting.

I could eat meatless Mexican food every day of the week. How about you?

More vegetarian Mexican recipes:

• Spicy Greens and Lentil Tacos with Guacamole Sauce.
• Sweet Potato Tacos with Arugula and Avocado Crema.
• Amazing Spinach and Black Bean Enchiladas.

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• Follow me on Instagram!
• Peruse my Pinterest boards for more vegetarian recipe ideas.
• Find daily vegetarian and healthy living ideas on my Facebook page.

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5 from 2 votes

Caramelized Onion and Arugula Tostadas

Serve these corn tortilla treats as snacks, or with a green salad for a simple supper.  Vegans–skip the cheese and yogurt garnish. Makes 4 (6-inch) or 10 smaller (4-inch) tostadas.

Prep Time15 minutes mins

Cook Time1 hour hr

Total Time1 hour hr 15 minutes mins

Course: Appetizer, Main Course

Cuisine: Mexican, Vegetarian

Keyword: vegetarian, tostadas, caramelized onions

Servings: 4 6-inch tacos or 10 (4-inch) tostadas.

Author: Letty | @lettyskitchen

Ingredients

• 2 ¼ pounds sweet onions, thinly sliced, 3 large or 5 smaller onions (see note)
• 2 tablespoons olive oil
• sea salt
• 4 (6-inch) corn tortillas or 10 (4-inch) corn tortillas
• cooking spray, as needed
• 1 ½ cups arugula, chopped (see note)
• salsa, homemade or purchased, as needed (see note)
• 1 tomato, diced
• 1 large avocado, diced in ½ inch cubes
• 1 lime, cut in wedges
• Chopped cilantro, as needed
• Grated white cheddar cheese, optional
• Whole milk plain yogurt, optional
• Guacamole avocado lime sauce optional

Instructions

• Heat the oil in a heavy bottomed skillet. Add the onions and cook over medium-high heat, stirring occasionally, until most of the moisture evaporates, 15 to 20 minutes.
• Reduce the heat to medium-low. Continue to cook, stirring occasionally, until the onions are very soft and a caramel brown color, about 1 hour. The onions will have reduced to about 1 ½ cups. (see note)
• Stir in a few pinches of salt. Set aside. (If you wish, cook the onions ahead of time, saving them for later, or the next day.)
• Preheat oven to 350° F. Spray both sides of the tortillas with cooking spray. Toast in the oven until crisp, 10 minutes or so.

To assemble:

• Distribute the caramelized onions, using your fingers to spread them around on the tortillas. Sprinkle with shredded arugula. Spoon some salsa over the arugula, and then scatter with diced tomatoes and avocado.
• Squeeze a lime wedge on top of the vegetables and sprinkle with chopped cilantro. If dairy is in your diet, finish with cheese and drizzles of plain yogurt.

Notes

• Prep ahead: Caramelize the onions ahead and you can have these tostadas ready in 20 minutes.
• Look for Walla-Walla, Vidalias, or other “sweet” onion varietals. Sweet onions caramelize well because of their higher percentage of natural sugar.
• I used the medium (4 mm) slicing blade that came with my food processor to slice the onions. I got a little teary-eyed, but not near as much as I would have slicing the onions by hand.
• Total raw onion weight needed—2 ½ pounds, which should yield about 8 cups sliced onions. That seems like a lot–but by the time the onions are caramelized you will wonder if you have enough.
• Substitute a different peppery or bitter green for the arugula, or just use shredded lettuce.
• If the onions start to brown too quickly, turn down the heat; don’t hurry the slow-cooked caramelization.
• Make them vegan: Skip the cheese and yogurt–drizzle your tostadas with guacamole avocado sauce.
• My homemade tomato salsa recipe here.

Nutrition

Calories: 208kcal | Carbohydrates: 32g | Protein: 4g | Fat: 8g | Saturated Fat: 1g | Sodium: 36mg | Potassium: 453mg | Fiber: 4g | Sugar: 14g | Vitamin A: 434IU | Vitamin C: 18mg | Calcium: 87mg | Iron: 1mg

Did you make this recipe?Mention @lettyskitchen or tag #lettyskitchen

Nutrition information is meant to be an estimate only. The numbers do not include the cheese, avocado and sauce. Numbers will also vary based on the brands you use and substitutions you made, and how many tostadas you actually eat.