Preheat the oven to 350°F.

In a large skillet, heat olive oil over medium heat. Add the diced onion and minced garlic, sautéing until the onion is translucent, about 3-4 minutes.

Add the ground beef, cooking until browned and fully cooked, breaking it apart with a spoon as it cooks. Drain excess fat if necessary.

Stir in the sliced zucchinis, diced tomatoes (with their juice), Italian seasoning, salt, and black pepper. Cook for an additional 5-7 minutes, until the zucchinis are slightly tender.

Transfer the mixture to a greased 9x13-inch baking dish. Sprinkle the mozzarella and Parmesan cheese evenly over the top.

Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly.

Let it cool for about 5 minutes before serving.