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