Sauté onion and bell pepper in hot oil in a large skillet over medium-high heat 5 minutes or until tender. Stir in chicken and next 7 ingredients; remove from heat.
Tear tortillas into 1-inch pieces; layer one-third of tortilla pieces in bottom of a lightly greased 13- x 9-inch baking dish. Top with one-third of chicken mixture and 2/3 cup cheese. Repeat layers twice.
Bake at 350° for 30 to 35 minutes.
Note: Freeze casserole up to 1 month, if desired. Thaw in refrigerator overnight, and bake as directed.