Preheat oven to 400°F (200°C) and lightly coat a 9x13 inch baking dish with non-stick spray.
Halve zucchinis lengthwise and use a spoon to scoop out the centers to create a channel, leaving a shell approximately 0.25-inch thick.
Finely chop 0.5 cup of the extracted zucchini flesh and set aside; discard the remaining flesh.
Heat olive oil in a large skillet over medium-high heat. Add ground turkey and cook until browned and internal temperature reaches 165°F.
Add diced onion, minced garlic, and the reserved chopped zucchini flesh to the skillet. Sauté for 5 minutes until vegetables are softened.
Incorporate the marinara sauce, oregano, salt, and black pepper. Reduce heat and simmer for 3 minutes.
Place the zucchini shells into the prepared baking dish. Distribute the turkey mixture evenly among the hollowed channels.
Top each boat with mozzarella and Parmesan cheese.
Bake for 25 minutes or until the zucchini is tender when pierced with a fork and the cheese is golden and bubbly.