1Preheat oven to 400. Coat an 8 X 8 inch baking dish with cooking spray.
2Cover bottom of dish with 1/2 cup salsa and top with four tortillas in a single layer (they will overlap), then layer with one-third of the spinach, cheese, chicken, black beans and remaining salsa. Repeat layers twice more, saving about 1/2 cup of the salsa and cheese to go on the top.
3Bake until golden brown, 20-25 minutes. Serve with sour cream, cilantro and avocado.