Preheat your oven to 375°F (190°C).

Lightly grease a baking dish large enough to hold the zucchini halves.

Wash and trim the ends of the zucchinis.

Slice each zucchini in half lengthwise.

Use a spoon to scoop out the center of each zucchini half, creating a hollow “boat.” Reserve the scooped-out zucchini flesh for the filling.

In a large skillet, heat the olive oil over medium heat.

Add the chopped onion and minced garlic, and sauté until softened (about 3-4 minutes).

Add the ground meat to the skillet and cook until browned, breaking it up with a spoon as it cooks.

Stir in the reserved zucchini flesh, marinara sauce, Italian seasoning, salt, and black pepper. Cook for an additional 5 minutes until the mixture is well combined and heated through.

If using breadcrumbs, stir them in at this point for added texture.

Spoon the filling mixture into the hollowed-out zucchini boats, dividing it evenly among them.

Place the stuffed zucchini boats in the prepared baking dish.

Sprinkle the shredded mozzarella and grated Parmesan cheese evenly over the stuffed zucchinis.

Cover the baking dish with foil and bake in the preheated oven for 25 minutes.

Remove the foil and bake for an additional 10-15 minutes, or until the zucchini is tender and the cheese is bubbly and golden.

Garnish with fresh parsley or basil if desired.

Serve the stuffed zucchini boats hot as a main dish or a hearty side.