Preheat oven to 325 degrees F. In a large saucepan, cook pepper and onion in melted margarine until tender, about 5 minutes.
Add soups, RO*TEL and chicken, stirring until well blended.
In a 13 x 9 x 2-inch baking pan, alternately layer tortillas, soup mixture and cheese, repeating for three layers. Bake 40 minutes or until hot and bubbling. Serves 8.