Step 1: Prepare the Zucchini Ribbons
Wash and dry your zucchini thoroughly. Trim off both ends. Using a mandoline slicer is highly recommended for this step to achieve thin, uniform slices. Set your mandoline to a ⅛-inch (about 3mm) thickness. Carefully slice the zucchini lengthwise into long, wide ribbons. If you don’t have a mandoline, you can use a wide vegetable peeler (like a Y-peeler) to create the ribbons, though they will be thinner. You will need approximately 40-48 good ribbons to make 20-24 ravioli.

Step 2: “Sweat” the Zucchini (Crucial Step)
Arrange the zucchini ribbons in a single layer on baking sheets lined with paper towels (you may need a few). Sprinkle the 1 teaspoon of salt evenly over all the ribbons. Let them sit for 20-30 minutes. You will see beads of moisture forming on the surface as the salt draws the water out. After 30 minutes, use paper towels to firmly pat both sides of each zucchini ribbon completely dry. This step is the secret to preventing a watery final dish.

Step 3: Prepare the Ricotta Filling
While the zucchini is sweating, prepare your filling. In a medium bowl, combine the whole milk ricotta, the thoroughly squeezed-dry spinach, ½ cup of Parmesan cheese, ½ cup of shredded mozzarella, the lightly beaten egg, minced garlic, chopped fresh basil, ½ teaspoon of salt, ¼ teaspoon of black pepper, and the optional red pepper flakes. Stir with a spatula until everything is just combined. Do not overmix.

Step 4: Prepare the Baking Dish
Preheat your oven to 400°F (200°C). Pour about 1 ½ cups of the marinara sauce into the bottom of a 9×13 inch baking dish and spread it evenly to create a base layer.

Step 5: Assemble the Zucchini Ravioli
Now for the fun part! To form each ravioli, take two of your dried zucchini ribbons and lay them on a clean work surface in a “plus sign” or “cross” shape, with one ribbon placed horizontally and the other vertically on top of it. Place a heaping tablespoon of the ricotta filling right in the center where the ribbons intersect. To enclose the filling, fold the ribbons over it, one at a time, starting with the bottom ribbon. Think of it like folding the flaps of a cardboard box: fold the bottom strip up, the top strip down, the left strip over to the right, and the right strip over to the left. This will create a neat little zucchini parcel.

Step 6: Arrange Ravioli in the Baking Dish
As you form each zucchini ravioli, gently place it seam-side down in the baking dish on top of the marinara sauce. Continue this process until you have used all of your filling. You should be able to arrange the ravioli snugly in a single layer in the dish.

Step 7: Top and Bake
Spoon the remaining 1 ½ cups of marinara sauce over and around the assembled ravioli. Drizzle the 1 tablespoon of olive oil over the top. Sprinkle evenly with the remaining 1 cup of shredded mozzarella cheese and an extra dusting of grated Parmesan cheese.

Bake, uncovered, for 20-25 minutes, or until the sauce is bubbly and the cheese is melted and starting to turn golden brown on top.

Step 8: Rest and Serve
Remove the baking dish from the oven and let it rest for at least 5-10 minutes. This allows the ravioli to set up and makes them easier to serve. Garnish with additional fresh basil leaves before serving.