Preheat the oven to 350°F (175°C).

In a large skillet, heat the 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 to the skillet, breaking it apart with a spoon. Cook until browned and cooked through, about 5-7 minutes. Drain any excess fat.

Stir in the drained diced tomatoes, Italian seasoning, salt, and black pepper. Cook for an additional 2-3 minutes until heated through.

In a greased 9x13 inch baking dish, layer half of the sliced zucchini on the bottom. Spread half of the beef mixture over the zucchini, then sprinkle with half of the cheddar cheese. Repeat the layers with the remaining zucchini, beef mixture, and top with the remaining cheese.

Evenly sprinkle the breadcrumbs over the top of the casserole.

Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and the breadcrumbs are golden brown.

Remove from the oven and let it cool for 5 minutes. Garnish with fresh parsley before serving.