Step 1: Preheat your oven to 375°F (190°C). Lightly grease a loaf pan or baking sheet to prevent sticking.
Step 2: Heat 1 tablespoon of oil in a skillet over medium heat. Add the chopped onions, bell peppers, and optional mushrooms and sauté for 3-4 minutes until softened. Stir in minced garlic and cook for another 30 seconds until fragrant. Remove from heat and let the vegetables cool slightly.
Step 3: In a large mixing bowl, combine 1½ lbs ground beef, ½ cup breadcrumbs, 2 lightly beaten eggs, ¼ cup milk, 1 tablespoon Worcestershire sauce, 1 teaspoon salt, ½ teaspoon black pepper, ½ teaspoon garlic powder, and ½ teaspoon onion powder. Mix gently until just combined—overmixing can make the meatloaf dense and tough.
Step 4: Stir in 1 cup shredded provolone or mozzarella cheese. Add the cooled sautéed vegetables and mix until evenly distributed.
Step 5: Transfer the meat mixture to the prepared pan and shape it into a loaf. Bake for 40-45 minutes, or until the internal temperature reaches 160°F (71°C).
Step 6: Remove the meatloaf from the oven and lay 4 slices of provolone cheese on top. Return to the oven for 5 minutes, or until the cheese is melted and bubbly. Optional: Broil for 1-2 minutes to slightly brown the cheese.
Step 7: Rest the meatloaf for 10 minutes before slicing—this helps retain its juices. Garnish with extra sautéed onions and peppers for added flavor. Serve with mashed potatoes, roasted veggies, or toasted hoagie rolls for a complete meal!