Preheat the oven to 350°F.

Fill a large, shallow pot or high-sided skillet with enough water to cover the noodles and bring to a boil. Salt the water then add the noodles and cook 3 minutes less than the package cooking directions. Transfer the noodles to a baking sheet drizzled with olive oil, lightly rolling the noodles so they don't stick. Cook the noodles in batches if needed.

While the noodles cook, mix the ricotta, beaten eggs, nutmeg, kosher salt, and black pepper in a small bowl. In a large bowl, add ¾ of the shredded cheese, thawed spinach, and the ricotta cheese mixture. Fold well to combine.

Pour half of the marinara sauce into a 9" X 13" baking dish.

Fill a gallon freezer bag with the cheese mixture, squeezing all of the filling into one corner of the bag. Twist the top of the bag to create a cone and cut off one corner of the bag. Make the cut large enough for the clumps of spinach in the filling to fit through. Pipe the filling in one end of the manicotti tube, then flip and repeat with the other end. Repeat with the rest of the noodles and arrange in rows in the baking dish.

Top the filled noodles with the rest of the marinara and shredded cheese. Sprinkle with the parsley. Spray a piece of aluminum foil with cooking spray and cover the dish taking care that the foil doesn't sit directly on the cheese. Bake for 30-40 minutes. Remove the foil for the last 10 minutes of baking if you like a lightly browned cheese. Garnish with more Parmesan and chopped parsley if desired.