Begin by preheating your oven to 375°F. Take the zucchini and wash them thoroughly. Afterward, trim off the stem ends and slice each zucchini lengthwise down the center. Use a spoon or a melon baller to scoop out the soft flesh from the middle, leaving a sturdy border of about 1/4 to 1/2 inch. Chop the scooped-out zucchini flesh into small pieces and set it aside for later use.

Arrange the hollowed-out zucchini halves on a parchment-lined baking sheet. Lightly brush the insides of the zucchini with 1/2 tablespoon of cooking oil and season them with 1/4 teaspoon of salt and 1/4 teaspoon of freshly cracked black pepper. Place the zucchini in the preheated oven and bake for 15 minutes. Once done, remove them from the oven and let them cool slightly.

While the zucchini are baking, prepare the filling. Heat a large skillet over medium heat, adding 1 tablespoon of oil to the pan. Once hot, add the Italian ground sausage and cook until it browns.

When the sausage is nicely browned, add the diced onion and minced garlic to the skillet. Continue cooking on medium heat until the onion becomes translucent and the garlic releases its aroma.

Into the skillet, stir in the Italian seasoning, 1/2 teaspoon of salt, 1/4 teaspoon of black pepper, garlic powder, marinara sauce, breadcrumbs, and half of the chopped zucchini flesh that you set aside earlier. Allow the mixture to simmer on medium-low heat for about 5 minutes, letting the flavors meld together.

Spoon the sausage mixture into the pre-baked zucchini boats, filling them generously. Top each boat with shredded mozzarella cheese, ensuring an even distribution. Return the zucchini boats to the oven and bake for an additional 15 minutes, or until the cheese has melted and the sausage filling is bubbling at the edges.

Finish by garnishing the zucchini boats with freshly chopped parsley, and serve immediately. Enjoy this delicious and hearty dish!