Preheat oven to 325°F. Spray 13x9-inch baking dish with cooking spray; set aside.
Melt butter in large saucepan over medium heat. Add bell pepper and onion; cook and stir about 5 minutes or until tender. Stir in both soups, undrained tomatoes and chicken.
Layer one-half each of tortillas, chicken mixture and cheese evenly in dish. Repeat layers again. Bake uncovered 40 minutes or until hot and bubbly.