Step 1: Prepare the Zucchini

1. Preheat the oven to 375°F (190°C).
2. Slice zucchinis in half lengthwise and scoop out the insides with a spoon. Reserve 1/2 cup of the zucchini flesh.
3. Brush the hollowed zucchinis with olive oil, season with salt and black pepper.
4. Place in a baking dish and bake for 10 minutes.

Step 2: Cook the Beef Filling

1. In a skillet, heat olive oil over medium heat.
2. Add chopped onion and garlic, sauté until fragrant (about 2 minutes).
3. Stir in ground beef, breaking it apart, and cook until browned.
4. Mix in the reserved zucchini flesh, diced tomatoes, red pepper flakes, Italian seasoning, paprika, salt, and pepper. Cook for another 5 minutes.
5. Stir in cooked rice or quinoa, if using. Remove from heat and mix in half of the shredded cheese.

Step 3: Assemble and Bake

1. Spoon the beef mixture into the zucchini boats evenly.
2. Top with remaining mozzarella and Parmesan cheese.
3. Cover with foil and bake for 20 minutes.
4. Remove foil and bake 5-10 more minutes until the cheese is melted and bubbly.

Step 4: Garnish and Serve

1. Remove from oven and let cool for a few minutes.
2. Sprinkle with fresh parsley before serving.
3. Enjoy warm!