Make the sauce/marinade:

Place all ingredients for the sauce in a food processor and pulse until finely chopped and mixed well. Mix 2 tablespoons of the sauce with 1 tablespoon olive oil and 1 tablespoon white vinegar and pour over the mushrooms. Marinate the mushrooms for at least 15 minutes. (can be overnight)

Make the filling:

Preheat the broiler and place mushrooms on a pan.  Broil for 5 minutes per side. Remove from heat and allow to cool slightly. Heat a tablespoon of olive oil in a skillet over medium heat and sauté the onions and and chili peppers.  Add a sprinkling of salt and cook about 10 minutes. Stirring often.

Prepare the Tacos: Slice the mushrooms. Heat tortillas, the best way is to place them directly on a gas burner and let them char, otherwise you can put them in a a hot frying pan for 30 seconds.

Place peppers and onions and then mushrooms on the taco, top with extra sauce and sliced avocados.