Preheat the oven to 190°C and lightly oil a medium baking dish.
Slice the zucchini lengthwise and scoop out the centers, leaving a firm border. Chop the removed zucchini flesh.
Arrange the zucchini halves in the baking dish. Brush them with olive oil and season with salt and pepper.
Heat the olive oil in a large skillet over medium-high heat. Cook the onion for 3 minutes, then add the garlic.
Add the ground beef and cook until browned, breaking it into small crumbles. Drain excess fat if needed.
Stir in the chopped zucchini, tomato sauce, tomato paste, Italian seasoning, smoked paprika, red pepper flakes, salt, and pepper. Simmer for 5 minutes.
Spoon the beef mixture into the zucchini shells. Sprinkle evenly with mozzarella and Parmesan cheese.
Bake uncovered for 20 to 25 minutes, until the zucchini is tender and the cheese is melted and lightly golden. Rest for 5 minutes, then garnish with fresh herbs.