Preheat oven to 350°F. Melt butter in a large skillet over medium heat. Add onion and serrano pepper. Cook and stir 4 to 5 minutes or until tender. Combine onion mixture, rice, turkey, corn, tomato sauce, chili powder, and cayenne pepper in a large bowl. Transfer to a greased 2-quart casserole. Cover and bake 40 minutes. Sprinkle with cheese. Bake 5 more minutes or until cheese is melted. Let stand 10 minutes before serving. Serve rice mixture over lettuce with bell pepper, avocado, jicama and lime wedges, if desired.