Prepare the Zucchini:
Preheat your oven to 375°F (190°C).
Slice the zucchinis in half lengthwise and scoop out the centers using a spoon or melon baller, creating zucchini "boats." Reserve the scooped-out flesh for later use.
Lightly brush the zucchini halves with olive oil and place them in a baking dish.
Cook the Filling:
Heat olive oil in a skillet over medium heat. Add the diced onion and cook until softened, about 3-4 minutes.
Add the minced garlic and cook for 1 minute until fragrant.
Stir in the ground beef, breaking it apart with a spoon, and cook until browned.
Add the reserved zucchini flesh, crushed tomatoes, Italian seasoning, smoked paprika, red pepper flakes, salt, and pepper. Cook for 5-7 minutes until the mixture thickens slightly.
Stuff the Zucchini:
Spoon the beef mixture evenly into the zucchini boats.
Sprinkle mozzarella and Parmesan cheese over the top.
Bake the Zucchini:
Cover the baking dish with foil and bake for 20 minutes.
Remove the foil and bake for an additional 10-15 minutes, or until the cheese is golden and bubbly.
Serve:
Garnish the stuffed zucchinis with fresh parsley.
Serve warm with a side salad or crusty bread.