Step 1: Prepare the Zucchini Boats
Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper or lightly grease a baking dish. Using a spoon or a melon baller, carefully scoop out the seedy center of each zucchini half, leaving a ¼-inch thick shell to form a “boat.” Place the zucchini boats on the prepared baking sheet. Brush the insides lightly with olive oil and season with a pinch of salt and pepper.

Step 2: Par-Bake the Zucchini (Optional but Recommended)
Place the zucchini boats in the preheated oven and bake for 10-12 minutes. This step removes excess moisture and starts the cooking process, preventing a soggy final dish. Remove from the oven (keep the oven on) and carefully tip any accumulated water out of the boats or off the sheet.

Step 3: Prepare the Filling
In a large mixing bowl, combine the shredded chicken, pesto, ricotta cheese, ¼ cup of the Parmesan cheese, minced garlic, Italian seasoning, and the egg (if using). Mix until well combined. Gently fold in the quartered tomatoes. Taste the mixture and season with salt and pepper as needed.

Step 4: Fill the Boats
Spoon the chicken pesto filling generously into the par-baked zucchini boats, dividing it evenly among them. Press the filling down gently and mound it slightly.

Step 5: Add the Cheese Topping
In a small bowl, combine the shredded mozzarella and the remaining ¼ cup of Parmesan cheese. Sprinkle this cheese blend evenly over the top of each filled zucchini boat. For extra crunch, sprinkle optional pine nuts or walnuts over the cheese.

Step 6: Bake Until Golden and Bubbly
Return the baking sheet to the oven. Bake for 18-22 minutes, or until the zucchini is fork-tender, the filling is hot, and the cheese is melted, bubbly, and golden brown on top.

Step 7: Broil (Optional)
For an extra-golden top, switch the oven to broil for the final 1-2 minutes, watching closely to prevent burning.

Step 8: Garnish and Serve
Remove from the oven and let the boats cool for 5 minutes. This allows the filling to set slightly. Garnish with fresh sliced basil. Serve hot, as a main course.