Bring a large pot of salted water to a boil. Cook lasagna noodles according to package directions for al dente. Drain, rinse with cold water, and lay noodles out in a single layer on a sheet of parchment paper to cool and to keep them from sticking together.
Meanwhile, thaw the spinach in a microwave safe bowl using the defrost setting or very low power in the microwave. (Alternatively, you can put the frozen spinach in the refrigerator the day before to thaw overnight.) Then wrap spinach in a clean kitchen towel and squeeze out the excess moisture.
Preheat oven to 350° F.
Crack the egg into a large bowl and use a fork to beat the egg slightly. To the bowl, add the spinach, ricotta cheese, all but 1 cup of the mozzarella, the Parmesan, salt and pepper. Stir until well combined.
Spread 1 cup of the marinara sauce in the bottom of a large rectangular baking dish, such as a 13x9-inch dish. Spread ¼ cup of the cheese and spinach mixture evenly over each of the lasagna noodles. Roll up and place, seam side down, in the prepared baking dish.
Spread remaining sauce over the tops of the roll ups and sprinkle on the remaining mozzarella cheese. (If you have extra marinara sauce, save it for serving with the roll ups.)
Cover the dish with foil (you can spray the underneath side of the foil with cooking spray to prevent it from sticking to the cheese). Bake for 30 minutes and then uncover and bake for 5 to 10 minutes more, until cheese is melted and lightly browned.