Using a pressure cooker: Heat the oil in the pot over medium flame. With the Instant Pot, use the Sauté button. Add the onion and celery; cook and stir until the onion is translucent, about 10 minutes. Stir in the garlic and cook the vegetables a few more minutes.
Rinse the black-eyed peas and add them to the pot, along with the water, tomatoes, bay leaves, oregano and red pepper flakes. The liquid should just cover the beans.
Using a pressure cooker: Cook 16 minutes under pressure, remove from heat and allow pressure to release naturally. Using an Instant Pot, turn the top dial to Seal and set the timer for 16 minutes. Allow pressure to release naturally.
For regular stove-top cooking: Rinse the beans and put them in a bowl, covering them amply with cold water. Let soak at least 6 hours or ideally, overnight. Follow directions for sautéeing the onions and celery and garlic, then add the broth and seasoning. Bring to a boil; reduce to a slow simmer and cover. Cook two hours or so, topping with water as needed, until the beans are tender to a bite. Continue with the directions for the collard greens and final flavor add-ins.
If adding fake soysage, heat a tablespoon of olive oil in a skillet. Cook the "sausage", breaking it into chunks with a spoon, until the “meat” is brown on several sides. Set aside.
Stack the collard leaves one on top of the other and roll into a tube shape. Slice ¼-inch thick into ribbons. Or simply chop into one-inch square pieces.
Add the collard ribbons to the pot. Simmer until the greens are tender, about 10 minutes. With the Instant Pot, use the Sauté button.
Add the reserved cooked “sausage”, if using. Stir in the apple cider vinegar and season to taste with more salt and pepper. (Amount of salt added wil depend on how salty the vegetable broth. If you use water instead, add about 3/4 teaspoon salt, to taste.)