Preheat oven to 375. Prepare a 2-quart casserole dish with cooking spray; set aside. In a large saucepan, heat oil over medium heat. Add chicken, onions, and bell peppers. Cook until chicken is longer pink and vegetables are tender. Stir in corn, hash browns, milk, salt, and black pepper. Cook until hash browns are lightly browned. Place mixture into prepared dish. Bake, covered, for 30 minutes or until heated through. Top with cheddar cheese. Bake for three minutes more, or until cheese has melted.