Heat the oven to 400°F. Lightly oil a 9x13-inch baking dish. Halve each zucchini lengthwise and scoop out the flesh with a tablespoon or melon baller, leaving a 1/4-inch shell. Reserve 1 cup of the scooped flesh, chopped; discard (or snack on) the rest. Arrange the boats cut-side up in the dish and sprinkle lightly with salt.

Heat the olive oil in a large skillet over medium-high heat. Add the ground turkey and cook, breaking it into crumbles, until no pink remains, about 5–6 minutes. Drain off any excess liquid. The turkey should reach 165°F internally — it will, well before the end.

Stir in the onion and cook 2 minutes until softened. Add the garlic, the chopped zucchini flesh, oregano, basil, red pepper flakes (if using), salt, and black pepper; cook 2 minutes more, until fragrant. Stir in the marinara and 1/4 cup of the Parmesan; simmer 1 minute. The filling should look thick and saucy, not soupy.

Spoon the turkey filling evenly into the zucchini shells, mounding it slightly — roughly 1/2 cup per boat.

Sprinkle the mozzarella evenly over the boats, then the remaining 1/4 cup Parmesan. Bake uncovered for 15 minutes, until the zucchini is fork-tender and the filling is bubbling.

Switch the oven to broil and broil the boats 1–2 minutes, watching closely, until the cheese is golden and lightly browned in spots. Rest 3 minutes, shower with fresh basil or parsley, and serve.