Heat oil in a large nonstick skillet over medium-high heat. Add onion, oregano, salt, pepper, and poblano, and sauté 5 minutes or until onion is tender. Add beans; cook 1 minute or until thoroughly heated. Remove from heat; stir in mango and avocado.
Place flour tortillas on a baking sheet coated with cooking spray. Arrange about 3/4 cup bean mixture on half of each tortilla, leaving a 1/2-inch border. Sprinkle 2 tablespoons cheddar cheese over bean mixture, and fold tortilla in half. Lightly coat tortillas with cooking spray. Broil 3 minutes or until cheddar cheese melts.