01 - Preheat oven to 400°F.
02 - Slice the zucchini in half lengthwise and scoop out the flesh, leaving a 1/2 inch shell. Reserve the scooped flesh and chop it.
03 - Place zucchini halves cut-side up in a baking dish. Drizzle with 1 tbsp olive oil and season lightly with salt and pepper.
04 - Heat remaining olive oil in a large skillet over medium heat. Add onion and cook until soft, about 3 minutes. Add garlic and cook 1 minute more.
05 - Add ground beef and cook, breaking it up, until browned. Drain excess fat if needed.
06 - Stir in chopped zucchini flesh, diced tomatoes, tomato paste, oregano, basil, salt, and pepper. Simmer for 5–7 minutes until mixture thickens.
07 - Spoon the beef mixture evenly into the zucchini boats. Top with mozzarella and Parmesan cheese.
08 - Cover baking dish with foil and bake for 20 minutes.
09 - Remove foil and bake an additional 8–10 minutes, until cheese is golden and bubbly.
10 - Garnish with fresh parsley or basil before serving.