Preheat the oven to 350°F.

Cut off the tops of the bell peppers, remove seeds and membranes, and chop the usable parts of the tops. Set aside.

Heat 2 tablespoons of olive oil in a skillet over medium-high heat. Cook the ground beef with salt and pepper until browned. Transfer to a plate.

In the same skillet, add the remaining olive oil, chopped bell pepper tops, and onions. Cook until softened. Add garlic and zucchini, cook for another minute.

Mix in the diced tomatoes and season with additional salt and pepper. Cook until heated through.

Combine the beef, cooked rice, and 1 1/2 cups of cheese with the vegetable mixture. Adjust seasoning if necessary.

Fill each bell pepper with the mixture and place them in a baking dish. Top with the remaining cheese.

Pour a small amount of water into the bottom of the dish, cover with foil, and bake for 30 minutes.

Remove foil and bake for an additional 15-20 minutes until peppers are tender and cheese is bubbly.