Rinse quinoa and bring to a boil with 1 1/2 cups of water (or broth) in a small pot. Cover, reduce heat to low and let quinoa cook for 15 minutes before removing from heat and fluffing cooked quinoa with a fork (or just cook according to package directions).
While quinoa cooks, melt coconut oil over medium-high heat. Add onions and bell pepper and sauté until peppers start to sear.
Add garlic, corn, and mushrooms and continue cooking until veggies are cooked and lightly browned.
Stir in salt, chili powder, paprika, cumin, half of the chopped cilantro, and 1/4 cup salsa. Add quinoa and black beans. Stir and remove from heat.
Serve veggie filling, grated cheese, additional salsa, cilantro, and avocado with lettuce using each leaf as a taco shell.
Notes
To make recipe vegan, leave out the cheese.
To make paleo or Whole30 compliant, leave out cheese and corn.
Leftover taco filling keeps well in a sealed container in the refrigerator for up to 4 days. Reheat before serving.