01 - Preheat oven to 400°F and line a baking dish with parchment paper or lightly grease it.
02 - Slice zucchinis lengthwise and use a spoon to scoop out centers, leaving 1/4-inch shells. Reserve and finely chop the scooped flesh.
03 - Heat olive oil in a large skillet over medium heat. Add onion and sauté for 2 minutes until translucent, then add garlic and cook for 30 seconds.
04 - Add ground turkey to the skillet, breaking it apart with a spatula. Cook until fully browned with no pink remaining, about 5 minutes.
05 - Stir in chopped mushrooms and reserved zucchini flesh. Cook 3 to 4 minutes until softened and moisture evaporates.
06 - Incorporate basil pesto, Italian herbs, red pepper flakes if using, salt, and pepper. Stir well and cook for 1 minute, then remove from heat.
07 - Arrange zucchini boats in the baking dish and spoon turkey-mushroom mixture evenly into each.
08 - Sprinkle mozzarella and Parmesan cheese over the filled zucchinis.
09 - Bake 18 to 22 minutes until zucchinis are tender and cheese is melted and golden.
10 - Allow to cool slightly before serving. Garnish with extra pesto or fresh basil if desired.