Preheat oven to 450 degrees F. Lightly coat a 9-inch pie plate with cooking spray; set aside. Place beans in a small bowl; use a fork to slightly mash the beans. In a small saucepan or skillet cook and stir beans over medium heat for 2 to 3 minutes or until heated through; set aside.
Spoon 1/4 cup of the salsa into bottom of prepared pie plate. Layer ingredients in the following order: one of the tortillas, half of the mashed beans, a second tortilla, all of the corn, 1/4 cup of the cheese, 1/4 cup of the salsa, a third tortilla, the remaining mashed beans, the remaining tortilla, and the remaining 1/2 cup salsa.
Cover with foil; bake about 12 minutes or until heated through. Remove foil. Sprinkle with the remaining 1/4 cup cheese.
Bake, uncovered, about 3 minutes more or until cheese melts. Top with avocado and cilantro. If desired, serve with fat-free sour cream.