In a large skillet, combine the beans, tomatoes, chicken and onion powder. Bring to a boil. Reduce heat; simmer, uncovered, for 5-8 minutes or until thickened.
In a small bowl, combine the cheeses. Sprinkle half of the cheese mixture over four tortillas. Layer with chicken mixture and remaining cheese mixture. Top with remaining tortillas.
In a large skillet over medium heat, cook quesadillas in 1 tablespoon oil for 1-2 minutes on each side or until cheese is melted, using additional oil as needed. Cut into wedges. Serve with sour cream, salsa and guacamole if desired.