Follow these step-by-step instructions to create perfectly baked, cheesy zucchini boats. Taking your time with each step, particularly in preparing the zucchini shells and building the filling, will ensure a delicious outcome.

1. Preheat Oven and Prepare Baking Dish: Preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch baking dish or a baking sheet large enough to hold the zucchini boats in a single layer without overcrowding. This prevents sticking and helps with even cooking.
2. Prepare the Zucchini Boats:
   • Wash and dry the zucchini thoroughly.
   • Trim off the stem ends of each zucchini.
   • Slice each zucchini in half lengthwise, creating two long “boat” shapes from each one.
   • Using a small spoon or a melon baller, carefully scoop out the flesh from the center of each zucchini half, leaving about a 1/4 to 1/2-inch thick shell. Be gentle to avoid puncturing the skin. The goal is to create a sturdy vessel for your filling.
   • Finely chop the scooped-out zucchini flesh (you should have about 1 cup) and set it aside. Discard any very large, tough seeds if your zucchini are on the larger side.
3. Sauté Aromatics and Zucchini Flesh:
   • Heat the olive oil in a large skillet or frying pan over medium heat.
   • Add the finely chopped onion and sauté for about 5-7 minutes, or until softened and translucent, stirring occasionally.
   • Add the minced garlic and cook for another minute until fragrant. Be careful not to burn the garlic, as it can become bitter.
   • Add the chopped zucchini flesh to the skillet. Cook for about 5-8 minutes, stirring occasionally, until it softens and some of the moisture has evaporated. This step is important to prevent a watery filling.
4. Create the Filling Mixture:
   • Remove the skillet from the heat and let the cooked vegetable mixture cool slightly for a few minutes. This prevents the egg from scrambling when added.
   • In a medium-sized mixing bowl, combine the sautéed onion, garlic, and zucchini flesh mixture.
   • Add the breadcrumbs, 1/4 cup grated Parmesan cheese, the lightly beaten egg, dried Italian herbs, salt, and freshly ground black pepper.
   • Mix everything together thoroughly until well combined. Taste a tiny bit (if comfortable doing so with raw egg, or just ensure seasonings are well distributed) and adjust salt and pepper if needed. The mixture should be moist but hold its shape.
5. Stuff the Zucchini Boats:
   • Arrange the hollowed-out zucchini shells cut-side up in the prepared baking dish.
   • Carefully and evenly spoon the prepared filling mixture into each zucchini boat. You can mound it slightly, as it will settle a bit during baking. Press the filling down gently to ensure it’s compact.
6. Add Cheese Topping:
   • Sprinkle the shredded mozzarella cheese generously over the top of each stuffed zucchini boat.
   • If desired, sprinkle a little extra Parmesan cheese on top of the mozzarella for added flavor and a golden crust.
7. Bake the Zucchini Boats:
   • Carefully place the baking dish into the preheated oven.
   • Bake for 25-35 minutes, or until the zucchini shells are tender (easily pierced with a fork) and the cheese topping is melted, bubbly, and golden brown. Cooking time may vary depending on the thickness of your zucchini shells and your oven’s calibration. If the cheese starts to brown too quickly before the zucchini is tender, you can lightly tent the dish with aluminum foil for the remainder of the baking time.
8. Rest and Garnish:
   • Once baked, remove the zucchini boats from the oven and let them rest for 5-10 minutes before serving. This allows the filling to set slightly and the cheese to cool down a bit, making them easier to eat.
   • If using, garnish with freshly chopped parsley or basil just before serving for a touch of freshness and color.