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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!

Caramelized Onion and Arugula Tostadas on baking sheet with lime wedges

  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.

closeup of Caramelized Onion and Arugula Tostadas on baking sheet

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.
onions in skillet for Caramelized Onion and Arugula Tostadas
caramelized onions in skillet for Caramelized Onion and Arugula Tostadas

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.

Caramelized Onion and Arugula Tostadas

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

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If you like this recipe, I’d be grateful if you’d give a ✮✮✮✮✮ rating on the recipe card below.

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.

Nutrition Facts
Caramelized Onion and Arugula Tostadas
Amount Per Serving
Calories 208 Calories from Fat 72
% Daily Value*
Fat 8g12%
Saturated Fat 1g6%
Sodium 36mg2%
Potassium 453mg13%
Carbohydrates 32g11%
Fiber 4g17%
Sugar 14g16%
Protein 4g8%
Vitamin A 434IU9%
Vitamin C 18mg22%
Calcium 87mg9%
Iron 1mg6%
* Percent Daily Values are based on a 2000 calorie diet.


  • Patricia

    Looks like a yummy recipe. We’re home and feeling very melancholy about the destruction in Baja and specifically feeling sad for Jim and Cita and what they have lost. Odd that this would occur to them and Andy and Nick having a fire in their house only a week before. Maybe carmelized tacos can sooth the sorrow. Love You Both, Patricia Reply · 23 September, 2014

    • Letty

      Thanks Patricia. Yes, Cynthia and Jim are in our hearts. I am putting together a list of where to donate aid $ for Baja. Reply · 23 September, 2014

  • Mona

    I am headed to the store to get the ingredients for the caramelized onion tacos with healing thoughts flowing through me and out to Baja. Love this Letty and thanks for all the magical recipes which are truly a form of art. Reply · 23 September, 2014

    • Letty

      How did Todos Santos “weather” Odile? Reply · 23 September, 2014

      • Mona

        Lots of damage, but not as bad as Cabo. Some friends lost everything and others faired pretty well. Electricity is still out in town, and the roads are policed to prevent looting. We had quite a bit of water but amazingly the palapa stayed in tact. Tough for those who are there with much recovery in the forecast . Reply · 23 September, 2014

  • Everything about these tostadas is making my mouth water! I am obsessed with caramelized onions, and arugula is one of my favorite greens! These are definitely a must-make!! Reply · 24 September, 2014

    • letty

      Thanks Julia,
      We got another huge Walla Walla (and arugula) in our CSA box this week–I’m making these again! Reply · 24 September, 2014

5 from 2 votes (2 ratings without comment)

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