Preheat the oven to 375°F (190°C).
In a skillet, brown the ground beef over medium heat.
Add diced onion and garlic to the skillet, cooking until soft.
Stir in the diced tomatoes, oregano, salt, and pepper.
In a large baking dish, layer half of the sliced zucchini on the bottom.
Spread the meat mixture over the zucchini layer.
Top with the remaining zucchini slices and sprinkle with cheese.
Sprinkle breadcrumbs over the cheese and drizzle with olive oil.
Cover the dish with foil and bake for 25 minutes.
Remove the foil and bake for an additional 15-20 minutes, until the top is golden.
Let the dish cool for 5 minutes before serving.