Preheat oven to 375° and spray a large baking dish with non-stick cooking spray.
Make the noodles:
Using a vegetable peeler, slice each zucchini into thin flat strips, peeling until you reach the center. These are your “noodles.”
Place sliced zucchini on a paper towel-lined baking sheets and sprinkle with salt. Allow zucchini to sit for about 1/2 an hour to let any water from the zucchini drain away.
Make the filling:
In a medium bowl, combine ricotta, Parmesan, egg, 2 tablespoons basil, garlic, and season with salt and pepper.
Assembly:
Lay two strips of zucchini noodles so that they overlap lengthwise. Lay two more noodles on top, perpendicular to the first strips. You should end up with a “T” shape. Spoon about 1 tablespoon of filling in the center of the zucchini. Bring the ends of the strips together to fold over the center, working one side at a time. Turn ravioli over and place in the baking dish seam-side down. Repeat with remaining zucchini and filling. Pour marinara around zucchini and top ravioli with mozzarella.
Bake 25 to 30 minutes.
Top with remaining basil and Parmesan before serving.