This one-pot meal is quick, easy, and delicious.
Preheat oven to 400 degrees. In a large skillet, heat 1 tablespoon olive oil over medium-high. Add onion and cook, stirring occasionally, until browned and soft, 6 minutes. Transfer to a plate and add 1 tablespoon oil to skillet. Add squash and bell peppers and cook until crisp-tender, 7 minutes. Return onion to skillet and add black beans and chili powder; stir to combine.
Meanwhile, wrap tortillas in foil and heat in oven 8 minutes. Serve tortillas with bean mixture, sour cream, and salsa.