1. Spray a large skillet with cooking spray and heat over medium-high. Saute onion, oregano, salt, pepper, and poblano until onion is tender (3-5 minutes).
2. Add beans and cook until heated (1 minute). Remove from heat and stir in mango and avocado.
3. Place tortillas on a baking sheet coated with cooking spray. Divide filling between tortillas, sprinkle with cheese, and fold in half. Lightly coat tortillas with cooking spray.
4. Set the broiler to high and place the rack in the top position. Broil, flipping once, until cheese melts and both sides are golden (2-3 minutes per side).