Preheat the oven to 375 degrees and line a baking sheet with parchment paper.
In a large bowl, combine the Italian sausage, ground beef, egg, Parmesan cheese, diced bell peppers, minced garlic, Italian seasoning, salt, and black pepper.
Mix the ingredients with your hands until just combined, then divide the mixture into four equal portions and shape each into a small loaf.
Place the mini meatloaves on one side of the prepared baking sheet.
Toss the trimmed asparagus with olive oil on the other side of the baking sheet and spread it in a single layer.
Bake for 25 minutes, then sprinkle the mozzarella cheese over the meatloaves and return the pan to the oven for 5 more minutes until the cheese melts and the internal temperature of the meatloaves reaches 160 degrees.
Remove from the oven and let the meatloaves rest for 5 minutes before serving with the roasted asparagus.