Preheat your oven to 375°F (190°C).

Wash and trim the ends off the zucchinis, then slice them in half lengthwise.

Using a small spoon or a melon baller, scoop out the center of each zucchini half, creating a boat shape. Leave about 1/4 inch of flesh intact to support the filling.

In a large skillet, heat a tablespoon of olive oil over medium heat.

Add the diced onions and minced garlic, sautéing until the onions are translucent.

Add the ground beef to the skillet, breaking it up with a spatula. Cook until browned, seasoning it with salt, pepper, and Italian seasoning.

Once the beef is cooked through, stir in the marinara sauce, allowing it to heat for about 2-3 minutes. Adjust seasoning if necessary.

Spoon the beef mixture evenly into each zucchini half, pressing down gently to pack the filling.

Top the filled zucchini boats with shredded mozzarella cheese, covering them generously.

Place the stuffed zucchini boats on a baking tray lined with parchment paper for easy cleanup. Bake in the preheated oven for about 25-30 minutes or until the zucchinis are tender and the cheese is bubbly and golden brown.

Remove from the oven and let cool for a few minutes before serving. Garnish with fresh basil if desired.