01 - Preheat oven to 400°F and line a baking dish with parchment paper.
02 - Cut zucchinis in half lengthwise and use a spoon to scoop out the centers, leaving about a 1/4-inch border to form boats. Roughly chop the scooped zucchini flesh and set aside.
03 - Brush zucchini boats with 1 tbsp olive oil, season with salt and pepper, and place cut side up in the baking dish. Bake for 10 minutes until slightly softened.
04 - Heat remaining olive oil in a large skillet over medium heat. Add onion and sauté until translucent, about 3 minutes. Add garlic and cook for 30 seconds more.
05 - Add ground beef to the skillet and cook until browned, breaking up clumps with a spoon, about 5 minutes. Drain excess fat if needed.
06 - Stir in chopped zucchini flesh, diced tomato, tomato paste, oregano, and basil. Cook for 4 to 5 minutes until vegetables are softened. Season with salt and pepper.
07 - Remove zucchini boats from the oven and fill each one with the beef mixture, packing gently.
08 - Sprinkle mozzarella and Parmesan evenly over each stuffed boat.
09 - Return to the oven and bake for 18 to 20 minutes, or until cheese is melted and lightly browned.
10 - Garnish with fresh chopped parsley before serving, if desired.