01 - Preheat the oven to 400°F. Lightly grease a large baking dish.
02 - Slice each zucchini in half lengthwise. Using a spoon, scoop out the flesh to create boats, leaving about 1/4-inch border. Chop the scooped flesh and set aside.
03 - Heat olive oil in a large skillet over medium heat. Add the onion and cook for 2–3 minutes until slightly softened.
04 - Add garlic and cook for 30 seconds, then add ground turkey. Cook, breaking up with a spoon, until browned and cooked through, about 5–6 minutes.
05 - Stir in the chopped zucchini flesh, spinach, cherry tomatoes (if using), oregano, red pepper flakes, salt, and black pepper. Sauté until spinach is wilted and excess moisture evaporates, 2–3 minutes.
06 - Remove from heat. Stir in basil pesto, half the mozzarella, and half the Parmesan. Mix in parsley and basil.
07 - Arrange zucchini boats in the prepared baking dish. Spoon the turkey-spinach mixture evenly into each boat.
08 - Sprinkle the remaining mozzarella and Parmesan over the tops.
09 - Bake for 20–25 minutes, until zucchini is tender and cheese is golden and bubbling.
10 - Garnish with extra herbs if desired. Serve warm.