Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the chopped onion and sauté for about 5 minutes until soft and translucent. Stir in the minced garlic and cook for an additional 1-2 minutes, then remove from heat and let cool.

In a large bowl, combine ground beef, ground Italian sausage, breadcrumbs, grated Parmesan cheese, chopped parsley, beaten eggs, milk, oregano, basil, salt, and pepper. Incorporate the cooled onion and garlic mixture gently but thoroughly.

In a separate bowl, blend ricotta cheese, some grated Parmesan, chopped basil, a beaten egg, salt, and pepper until smooth and creamy.

Prepare sun-dried tomatoes and finely chop them if needed. In the same skillet, add more olive oil and sauté the spinach for about 3 minutes until wilted.

Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper.

Take half of the meat mixture and press it onto your prepared baking sheet into a rectangle about 1 inch thick.

Spread the ricotta mixture over the pressed meat layer. Scatter the sautéed spinach and sun-dried tomatoes on top, followed by slices of fresh mozzarella.

Cover the filling with the remaining meat mixture, sealing the edges by pressing them together firmly, and shape into a loaf.

In the same skillet, sauté more minced garlic, then add crushed tomatoes, tomato sauce, water, oregano, basil, sugar, salt, and pepper. Simmer for 15-30 minutes.

Pour a portion of the sauce over the stuffed meatloaf and place it in the oven. Bake for 60-75 minutes until the internal temperature reaches 160°F (71°C).

Once baked, let the meatloaf rest for 10-15 minutes before slicing.