Follow these detailed steps carefully to ensure your pasta bake is perfectly cooked, full of flavor, and has the ideal texture—never watery, always wonderful.

Step 1: Prepare the Zucchini (The Most Important Step!)
First, preheat your oven to 375°F (190°C). Lightly grease a 9×13 inch (or equivalent 3-quart) baking dish. Using the large holes of a box grater, shred all of the zucchini. Place the shredded zucchini in a colander set over a bowl or the sink. Sprinkle it generously with about 1/2 teaspoon of salt and toss to combine. Let it sit for 15-20 minutes. The salt will draw out a surprising amount of excess water. After it has rested, take large handfuls of the shredded zucchini and squeeze it firmly over the sink. You want to extract as much liquid as physically possible. This step is absolutely critical to prevent a watery pasta bake. Once squeezed, you should be left with a much smaller, denser volume of zucchini. Set it aside.

Step 2: Cook the Pasta
Bring a large pot of heavily salted water to a rolling boil. Add the pasta and cook according to package directions, but be sure to undercook it by about 2 minutes, so it is very “al dente.” The pasta will continue to cook in the oven, and this prevents it from becoming mushy. Once cooked, drain the pasta well but do not rinse it.

Step 3: Create the Flavor Base
While the pasta is cooking, heat the olive oil in a large skillet or Dutch oven over medium heat. Add the finely chopped onion and sauté for 5-7 minutes, until it becomes soft, translucent, and slightly sweet. Add the minced garlic and the optional red pepper flakes and cook for another minute until fragrant. Be careful not to burn the garlic.

Step 4: Build the Sauce
Pour the jar of marinara sauce into the skillet with the onions and garlic. Stir to combine. Bring the sauce to a gentle simmer, then reduce the heat to low. Stir in the dried oregano, the squeezed zucchini, and half of the chopped fresh basil. Let the sauce simmer gently for 5-10 minutes for the flavors to meld together. This allows the zucchini to soften further and absorb the taste of the sauce. Taste and adjust seasoning with salt and pepper if needed.

Step 5: Mix the Creamy Cheese Filling
In a large mixing bowl, combine the whole milk ricotta, the lightly beaten egg, 1/2 cup of the grated Parmesan cheese, the remaining half of the chopped fresh basil, 1/2 teaspoon of salt, and 1/4 teaspoon of black pepper. Mix thoroughly until everything is smooth and well-incorporated.

Step 6: Combine and Assemble
Add the drained, al dente pasta to the large bowl with the ricotta mixture. Pour the zucchini-marinara sauce from the skillet over the pasta. Gently but thoroughly, fold everything together until the pasta is evenly coated in both the ricotta mixture and the marinara sauce. Every piece of pasta should be beautifully enveloped in creamy, saucy goodness.

Step 7: Layer and Bake to Perfection
Pour the pasta mixture into your prepared 9×13 inch baking dish and spread it into an even layer. Sprinkle the top evenly with the 2 cups of shredded mozzarella cheese, followed by the remaining 1/2 cup of grated Parmesan cheese.

Step 8: Bake the Casserole
Cover the baking dish tightly with aluminum foil. This traps the steam and helps the casserole cook through without drying out. Bake in the preheated oven for 25 minutes. After 25 minutes, carefully remove the foil. Return the dish to the oven and bake for another 15-20 minutes, or until the sauce is bubbly and the cheese on top is completely melted, golden brown, and slightly crispy in spots. For an even browner top, you can place it under the broiler for 1-2 minutes at the very end, but watch it like a hawk to prevent burning.

Step 9: Rest and Serve
Remove the pasta bake from the oven and let it rest on a wire rack for at least 10-15 minutes before serving. This is a crucial step that allows the casserole to set, making it much easier to slice and serve. Garnish with additional fresh basil before bringing it to the table.