1. Preheat oven to 350 degrees. Coat a 9x13 pan with cooking spray; set aside.
2. In a large skillet saute onion, bell peppers and garlic in olive oil over medium-high heat until tender.
3. Add chicken, tomatoes, condensed soup, chicken broth, cumin and chili pepper to skillet. Heat mixture through. Remove from heat.
4. Place 6 tortillas in the prepared baking dish, overlapping as necessary. Top with 1/3 of the chicken mixture and sprinkle with one cup of cheese.
5. Repeat layers twice more, leaving off the final layer of cheese.
6. Bake, covered for 25 minutes or until bubbly.
7. Bake, uncovered, about 5 minutes more and remove from oven.
8. Just before serving, top casserole with lettuce and chopped tomatoes.