This Chicken Philly Cheesesteak Spaghetti Casserole is a delicious twist on the classic Philly cheesesteak sandwich. Tender chicken, sautéed peppers and onions, and melted cheese are combined with spaghetti and baked to perfection. The result is a hearty and flavorful casserole that is sure to please the whole family. Serve it with a side salad for a complete meal.