Prep the zucchini:

Preheat oven to 375°F (190°C).

Slice zucchinis in half lengthwise and scoop out the center with a spoon, leaving about 1/4-inch thick shells.

Lightly brush or spray with olive oil, and place them in a baking dish, cut side up.

Bake for 10 minutes to soften.

Make the beef filling:

In a skillet over medium heat, cook ground beef until browned.

Add onion (if using) and garlic; cook until soft and fragrant.

Stir in marinara sauce, Italian seasoning, salt, and pepper.

Let simmer for 5 minutes to thicken.

Stuff and bake:

Spoon the beef mixture into the zucchini boats.

Top each with shredded mozzarella and a sprinkle of parmesan.

Return to oven and bake for 15–20 minutes, until cheese is bubbly and golden.

Serve:

Garnish with fresh parsley or basil if desired.

Enjoy hot, optionally with a dollop of sour cream or extra marinara on the side.