Preheat your oven to 375°F (190°C) to ensure it's ready for baking.
In a large mixing bowl, combine the ground beef and ground turkey. Add the breadcrumbs, egg, finely chopped onion, minced garlic, Italian seasoning, salt, and black pepper. Using your hands or a sturdy spoon, mix everything thoroughly until well incorporated for a consistent meat mixture.
Grease a 9x13 inch baking dish generously with cooking spray or a bit of oil. Evenly spread the meat mixture in the dish, pressing it down slightly to form an even layer that will serve as the base of your bake.
Place the meatloaf in the preheated oven and bake for 30 minutes, allowing the flavors to meld and the meat to set.
While the meatloaf is baking, prepare your mashed potatoes if you're making them from scratch. Blend in milk and sour cream until you achieve a smooth, creamy consistency.
After 30 minutes, carefully remove the meatloaf from the oven. Evenly spread the prepared mashed potatoes over the top of the meatloaf, using a spatula to create a smooth surface.
Generously sprinkle the shredded cheddar cheese over the mashed potatoes. If desired, add the crumbled bacon on top for a savory crunch.
Return the baking dish to the oven and bake for an additional 25-30 minutes, or until the cheese is melted, bubbly, and golden brown.
Once done, allow the dish to cool for about 10 minutes. This will aid in setting the layers for easier slicing.
Just before serving, drizzle barbecue sauce across the top for an extra zing and garnish with finely chopped green onions for a pop of color and freshness. Slice into squares and serve warm.
Notes
Feel free to customize the toppings with your favorite ingredients.