Preheat your oven to 375 degrees F. Line a baking sheet with parchment paper.

Wash the zucchini thoroughly and trim off the stem ends. Slice each zucchini in half lengthwise.

Using a spoon or melon baller, scoop out the center flesh of each zucchini half, leaving a 1/4 to 1/2-inch thick shell. Roughly chop the scooped-out flesh and set aside half of it for the filling; reserve the other half for another use.

Place the hollowed zucchini shells on the prepared baking sheet. Brush the insides with 1/2 tablespoon of olive oil and season with 1/4 teaspoon salt and 1/4 teaspoon black pepper.

Bake the zucchini shells for 15 minutes. Remove from the oven and set aside while you make the filling.

While the zucchini bakes, heat the remaining 1 tablespoon of olive oil in a large skillet over medium heat. Add the Italian sausage and cook, breaking it up with a spoon, until browned, about 5-7 minutes.

Add the diced onion and minced garlic to the skillet. Continue to sauté for 2-3 minutes until the onion is translucent and fragrant.

Stir in the Italian seasoning, remaining 1/2 teaspoon salt, remaining 1/4 teaspoon black pepper, garlic powder, marinara sauce, breadcrumbs, and half of the reserved chopped zucchini flesh. Mix well and let the mixture simmer over medium-low heat for 5 minutes.

Spoon the filling evenly into the pre-baked zucchini shells. Top each boat with shredded mozzarella cheese.

Return the baking sheet to the oven and bake for 15 minutes, until the cheese is melted and bubbly. Garnish with fresh chopped parsley if desired and serve warm.