1. Preheat oven to 375℉. Line a 9×5 loaf pan with parchment paper and set aside.
2. Make the filling: Melt the butter in a large skillet over medium-high heat. Add the bell pepper and onion then season with salt and pepper. Cook, stirring occasionally, until the bell peppers are soft and onions are lightly browned. Remove from heat and cool.
3. Make the meatloaf: In a large bowl, combine all ingredients and mix really well. Add half of the meat mixture to the prepared loaf pan and gently press into the bottom and sides of the pan.
4. Add the bell pepper mixture to the loaf pan and sprinkle with 2 ounces of American cheese. Top with remaining meat and gently press into the pan.
5. Bake the meatloaf in the preheated oven for 50-60 minutes, or until the meatloaf reaches an internal temperature of 160℉.
6. Make the topping: While the meatloaf bakes, add butter to a small saucepan and melt over medium-low heat. Add the American cheese, cream cheese, and milk to the melted butter and melt, stirring constantly, until smooth and creamy.
7. Take meatloaf from the oven and drain off the liquid fat. Allow the meatloaf to cool in the pan for 10 minutes then transfer to a cutting board. Pour half of the cheese sauce over the meatloaf.
8. Cut the meatloaf into thick slices and drizzle the remaining cheese sauce over each piece. Enjoy!