Heat the oil in a non-stick frying pan over medium-high heat.
In a bowl, toss the mushrooms, pepper and onion with chili powder and salt and pepper. Stir fry for 3–5 minutes, until veggies are soft. Return veggies to the bowl to cool.
To assemble the quesadillas, place ½ cup of the veggie mixture and ¼ cup of beans on 4 of the small tortillas. Sprinkle each tortilla with grated cheese and top with a second small tortilla.
In the same frying pan, cook each quesadilla over medium-high heat, flipping once, until the cheese melts and the tortilla is golden brown on each side.
Cut the quesadillas in wedges. Serve with salsa.
4 servings