01 - Set oven to 375°F to ensure proper cooking temperature.
02 - Cut zucchinis in half lengthwise. Scoop out the pulp with a spoon, leaving a 1/2 inch thick shell. Finely chop the reserved pulp and set aside.
03 - Heat olive oil in a large skillet over medium heat. Add onion and cook for 2-3 minutes until softened. Add garlic and continue cooking for 30 seconds until fragrant.
04 - Add ground beef to the skillet. Break up with a spoon and cook for 5-6 minutes until fully browned. Drain excess fat if necessary.
05 - Stir in chopped zucchini pulp, diced tomato, tomato paste, oregano, basil, salt, and pepper. Simmer for 4-5 minutes until well combined and most liquid has evaporated.
06 - Remove from heat. Mix in breadcrumbs, Parmesan cheese, and fresh parsley until evenly distributed throughout the beef mixture.
07 - Arrange zucchini halves in a baking dish. Fill each shell with the beef mixture, pressing down gently to pack the filling securely.
08 - Sprinkle shredded mozzarella cheese evenly over the tops of the stuffed zucchinis.
09 - Cover baking dish with aluminum foil and bake for 20 minutes to cook the zucchini through.
10 - Remove foil and continue baking for 10-15 minutes until cheese is golden brown and bubbly. Garnish with additional fresh parsley and serve immediately.