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 thick shell. Finely chop the pulp and set aside.
03 - Heat the olive oil in a large skillet over medium heat. Add the chopped onion and sauté for 2–3 minutes until softened. Add the minced garlic and cook for another 30 seconds until fragrant.
04 - Add the ground beef to the skillet. Cook, breaking it up with a spoon, until browned throughout, about 5–6 minutes. Drain excess fat if necessary.
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 has been absorbed.
06 - Remove the skillet from heat. Stir in the breadcrumbs, grated Parmesan, and fresh parsley until evenly distributed.
07 - Arrange the zucchini halves in a baking dish. Fill each shell with the beef mixture, pressing down lightly to pack the filling securely.
08 - Sprinkle the shredded mozzarella cheese evenly over the tops of the stuffed zucchini.
09 - Cover the baking dish with foil and bake for 20 minutes.
10 - Remove the foil and bake for an additional 10–15 minutes until the cheese is golden and bubbly.
11 - Garnish with additional fresh parsley and serve hot.