Preheat oven to 400 hundred degrees.
Spray two 9x13 baking dishes with a cooking spray.
In a large skillet over medium-high heat, brown ground Italian sausage.
Using a mini food processor or a knife, mince or chop the onion.
After browning the Italian sausage, add the minced onion.
Next, add the seasonings including, Italian seasoning, red pepper flakes, salt, pepper, and granulated garlic.
Stir in the Marinara Sauce. If you want to keep the recipe low carb, I have found the best low carb spaghetti sauce is Rao's. It is only two carbs in a half of cup and tastes delicious.
After stirring in the Marinara sauce, add the Mozzarella or Pizza cheese plus the Parmesan cheese.
Wash and cut the ends off the Zucchini.
Slice the Zucchini in half horizontally and scoop out the center and seeds with a small spoon.
Add the Zucchini to the baking dishes.
After adding the Zucchini to the baking dishes, fill each one with the Italian sausage filling.
Top the filling with the additional Mozzarella or Pizza cheese plus Parmesan cheese.
With the baking dish covered with foil, bake for 40 minutes. This will depend on how thick your zucchini are.
After 30 minutes remove the foil, stick a fork in them. The fork should easily into each zucchini boat.