In a large mixing bowl, combine ground beef and ground turkey with breadcrumbs, egg, chopped onion, minced garlic, Italian seasoning, salt, and black pepper. Mix until well incorporated.
In a greased 9x13 inch baking dish, spread the meat mixture evenly to form a meatloaf base.
Bake the meatloaf in the preheated oven for 30 minutes.
While the meatloaf is baking, prepare the mashed potatoes if using homemade. Mix the mashed potatoes with milk and sour cream for creaminess.
After 30 minutes, remove the meatloaf from the oven. Spread the mashed potatoes evenly over the meatloaf, smoothing the top with a spatula.
Sprinkle the shredded cheddar cheese evenly over the mashed potatoes, followed by the crumbled bacon if using.
Return the baking dish to the oven and bake for an additional 25-30 minutes, or until the cheese is bubbly and golden.
Once done, let it sit for about 10 minutes before serving to allow it to set.
Drizzle the top with barbecue sauce and garnish with chopped green onions before cutting into squares for serving.
Notes
Feel free to customize with your favorite toppings or add more vegetables.