01 - Preheat oven to 400°F. Line a baking sheet or large baking dish with parchment paper.
02 - Slice each zucchini in half lengthwise. Using a spoon, carefully scoop out the center flesh, leaving a 1/4-inch border to form a shell. Reserve 1/2 cup of the scooped flesh and finely chop it. Set aside.
03 - Drizzle the zucchini shells with olive oil and season with salt and pepper. Arrange cut side up on the prepared baking sheet.
04 - Heat a large skillet over medium heat. Add the ground turkey and cook for 3 to 4 minutes, breaking it apart with a spoon as it browns. Add the diced onion and minced garlic, sautéing until softened, about 2 minutes.
05 - Stir in the reserved chopped zucchini flesh, chopped spinach, dried oregano, dried basil, crushed red pepper flakes, salt, and black pepper. Cook for 3 to 4 minutes until the spinach is fully wilted and excess moisture has evaporated.
06 - Remove the skillet from heat. Add the basil pesto and stir until evenly combined with the turkey and spinach mixture.
07 - Spoon the pesto turkey and spinach filling evenly into each zucchini boat, mounding slightly. Sprinkle the shredded mozzarella and grated Parmesan evenly over the tops.
08 - Bake for 20 to 25 minutes until the zucchini shells are fork-tender and the cheese is melted and golden brown.
09 - Remove from the oven and garnish with torn fresh basil leaves. Serve immediately while hot.