01 - Set oven to 375°F.
02 - Cut zucchinis in half lengthwise. Scoop out pulp with a spoon, leaving a 1/2 inch shell. Chop the pulp and set aside.
03 - Heat olive oil in a large skillet over medium heat. Add onion and cook 2–3 minutes until soft. Add garlic and cook 30 seconds.
04 - Add ground beef to skillet. Cook, breaking up with spoon, until browned, about 5–6 minutes. Drain excess fat if needed.
05 - Stir in chopped zucchini pulp, diced tomato, tomato paste, oregano, basil, salt, and pepper. Cook 4–5 minutes until well combined and most liquid is absorbed.
06 - Remove from heat. Stir in breadcrumbs, Parmesan, and fresh parsley.
07 - Arrange zucchini halves in a baking dish. Fill each with beef mixture, pressing lightly to pack.
08 - Sprinkle mozzarella cheese evenly over tops.
09 - Cover with foil and bake 20 minutes.
10 - Remove foil and bake 10–15 minutes more until cheese is golden and bubbly.
11 - Top with extra parsley and serve hot.