1. Arrange racks in top and bottom thirds of oven and preheat to 400ºF. Line 2 large baking sheets with foil. Place tortillas on baking sheets and brush with oil. Bake until lightly browned, 4 to 5 minutes.
2. Divide chicken, beans and cheese among tortillas and return to oven. Bake until cheese has melted, 3 to 4 minutes. Remove from oven, top each portion with 1/4 of lettuce, salsa and sour cream. Serve immediately.