Preheat your oven to 350°F (175°C).
Cut the tops off the zucchinis and scoop out the flesh, leaving about 1/4 inch of zucchini around the edges.
In a skillet, heat olive oil over medium heat. Add the chopped onion and minced garlic. Sauté until they become translucent.
Add the ground meat and cook until browned.
Stir in the diced tomatoes, cooked rice, basil, and 2 tablespoons of Parmesan cheese. Season with salt and pepper to taste.
Fill each hollowed-out zucchini with the meat and rice mixture.
Place the stuffed zucchinis in a baking dish. Sprinkle the remaining Parmesan cheese on top.
Cover the dish with aluminum foil and bake for 20 minutes.
Remove the foil and bake for an additional 10 minutes, or until the zucchinis are tender and the cheese is golden brown.