Step 1

Preheat oven to 375 degrees F.

Step 2

Cook shells in a pot of boiling water according to package directions until al dente. Drain and transfer to a plate.

Step 3

Heat oil in a large skillet over medium heat. Add zucchini, onion and garlic and cook, stirring often, until the vegetables are softened, about 5 minutes. Add turkey and cook, breaking it up with a wooden spoon, until cooked through, 3 to 4 minutes.

Step 4

Whisk ricotta, 1/4 cup Parmesan, egg, Italian seasoning, fennel seed, nutmeg, crushed red pepper, salt and pepper in a large bowl. Add the turkey mixture and mix well.

Step 5

Spread 1 cup marinara in the bottom of a 9-by-13-inch baking dish. Spoon 2 heaping tablespoons of the ricotta mixture into each shell; arrange in the baking dish, seam-side up. Top the filled shells with the remaining 1 cup sauce and sprinkle with the remaining 1/4 cup Parmesan.

Step 6

Cover the baking dish with foil and bake until the marinara is bubbly, about 30 minutes. Uncover and bake for 10 minutes more. Let the shells rest for 10 minutes, then sprinkle with basil, if desired, and serve.