Preheat the oven to 375 degrees. Line a baking sheet with parchment paper.
In a large bowl, combine the ground beef, breadcrumbs, egg, Italian seasoning, onion, garlic, salt, and pepper. Mix until evenly blended.
Divide the mixture into four equal portions. Shape each into a small loaf and press a few mozzarella cubes into the center of each before sealing the meat around the cheese.
Place the loaves on the baking sheet and bake for 25 minutes until cooked through.
While the meatloaves bake, use a vegetable peeler to create thin ribbons from the zucchinis. Toss the ribbons with olive oil and a pinch of salt.
Warm the tomato sauce in a small saucepan over low heat.
Serve each meatloaf with a spoonful of tomato sauce and a pile of zucchini ribbons on the side.