1. Preheat oven to 375 F.
2. Cut each zucchini in half lengthwise and use a spoon to carefully scoop out the flesh to create a thick shell or “boat”, about 1/4 inch to ½ inch thick.
3. Place the zucchini in a row, cut side up, on a large sheet pan or casserole dish. Drizzle with olive oil and sprinkle with salt and pepper, to taste.
4. Bake for 15 minutes.

Prepare the filling:

1. Heat oil in a saucepan over medium-high heat until the oil is sizzling hot, about 1 minute.
2. Add ground beef and cook until browned on all sides, about 5 minutes. Use a spatula to break up the beef into small pieces to help even browning.
3. Add onion, garlic, Italian seasoning, salt, and pepper. Stir well and cook until fragrant, about 1 minute.
4. Stir in tomato sauce and reduce heat to low. Simmer for 5-10 minutes until thickened, then remove from heat. If it is too watery, continue to simmer until thickened.

Assemble and bake:

1. Fill each zucchini shell with equal amounts of meat sauce and top with equal amounts of mozzarella and parmesan cheese.
2. Bake for another 15 minutes, until zucchini is tender and cheese is melted and golden brown. You can also pop it into the broiler on high for 2-3 minutes at the end until the cheese is golden brown and bubbly.
3. Sprinkle chopped parsley on top and serve warm.