Preheat and Prepare: Start by setting your oven to 375°F (190°C) and ready your baking equipment. Lightly grease a 9x5-inch loaf pan.
Sauté Vegetables: In a nonstick pan, heat a small amount of oil. Then, sauté the chopped onions, diced bell pepper, and sliced mushrooms until they are soft and lightly browned. Next, add the minced garlic and cook for an additional minute; set aside to cool.
Mix the Meat: In a large bowl, combine the lean ground beef and ground turkey. Then, stir in the sautéed vegetables, low-fat sour cream, whole-grain breadcrumbs, Worcestershire sauce, dried oregano, salt, and pepper. Mix gently until everything is evenly distributed.
Layer the Cheese: Fold in the provolone cheese strips, ensuring they are evenly spread throughout the meat mixture. Next, add half of the shredded mozzarella cheese into the mix, saving the rest for topping later.
Form and Bake: Transfer the meat mixture into the prepared loaf pan, smoothing the top with a spatula. Sprinkle the remaining mozzarella cheese evenly on top. Then, bake in the preheated oven for 50 minutes, or until the internal temperature reaches 160°F (71°C).
Rest and Serve: Let the meatloaf sit for around 10 minutes after baking before slicing and serving. Finally, slice and serve warm, enjoying the robust flavors and creative twist on a classic dish.