Preheat the oven to 400 degrees F.

Carefully remove the middles of the zucchini with a melon baller or metal teaspoon measure, leaving 1/8 inch sides. Roughly chop the middles into smallish pieces; set aside.

Heat olive oil in a large, non-stick sauté pan over medium heat. Add onions, season with salt, and cook for 3 - 5 minutes until they start to look glassy; add garlic and sauté until fragrant, 30 - 60 seconds, stirring so the garlic doesn't burn. Add chopped zucchini, season with salt and pepper, and cook over medium-low heat until tender and any liquid has been absorbed, about 5 minutes. Set aside to cool.

Place the peppers and zucchini shells in a 9 x 13 inch baking dish that has been sprayed with cooking spray.

In a large bowl, lightly beat the egg with a fork. Add the cooled veggies and 1 1/2 teaspoons kosher salt and stir with your fork to combine. Add rice and 1/3 cup parmesan cheese and mix. Add the turkey and gently mix together with your fingers, just until evenly combined; do not over-mix or they will be tough.

With your hands, stuff the veggies with the turkey mixture. Pour marinara sauce over and sprinkle with 1/4 cup parmesan cheese.

Set baking dish on a cookie sheet and bake until the vegetables are tender and the top is golden brown. An instant read thermometer inserted into the filling should register 165 degrees, about 45 minutes.