Preheat oven to 450 degrees
Add mushrooms, onion, and bell pepper to a large glass casserole dish
Add salt, pepper, cumin, chili powder, garlic powder, onion powder, paprika and olive oil
Use your hands to mix until vegetables are evenly coated with oil and spices
Bake at 450 degrees for 15 minutes, then remove from oven to stir
Bake an additional 5-10 minutes, until roasted and caramelized
Once vegetables are done roasting, squeeze half of a lime over them and stir
Serve on corn tortillas with sliced avocado