1. Preheat oven to 400ºF. Line a baking sheet with heavy-duty foil. Mist both sides of tortillas with cooking spray. Place on sheet and bake until crisp, about 8 minutes.
2. Toss avocado with lime juice; season with salt. Spread some beans on each tortilla, top with chicken and avocado. Sprinkle with cheese. Return to oven and bake until warmed through, 7 to 10 minutes. Top with lettuce and salsa and serve immediately.