01 - Set oven to 400°F and prepare for baking.
02 - Slice zucchini lengthwise and scoop out the center, leaving a ½ inch shell. Chop the reserved flesh.
03 - Arrange zucchini halves cut-side up in a baking dish, drizzle with 1 tablespoon olive oil, then season lightly with salt and pepper.
04 - Heat remaining 1 tablespoon olive oil in a skillet over medium heat. Cook onion until translucent, about 3 minutes, then add garlic and sauté for 30 seconds.
05 - Add ground beef to the skillet, cook until browned and crumbled, 5 to 6 minutes. Drain excess fat if necessary.
06 - Mix in chopped zucchini flesh, diced tomato, tomato paste, oregano, basil, paprika, salt, and black pepper. Cook for 5 more minutes until mixture thickens and vegetables soften.
07 - Spoon the beef mixture evenly into zucchini shells and sprinkle shredded mozzarella over the top.
08 - Cover the baking dish with foil and bake for 20 minutes.
09 - Remove foil and bake an additional 5 to 10 minutes until the cheese is golden and bubbly.
10 - Sprinkle chopped parsley over zucchini boats before serving, if desired.