Preheat oven to 350. Cook onions and garlic in oil until soft. Turnoff heat; mix in chicken, corn, olives, chilies, and pepper flakes.
Remove tops from bell peppers, then slice in half lengthwise, removeseeds and membranes, and arrange around edge of casserole. Addcheese to chicken mixture and move immediately to casserole. Bake 45minutes.