Bring a large pot of salted water to a boil, then add the lasagna noodles. Cook until al dente, about 8-10 minutes. Drain and rinse with cold water. Lay flat to cool.

Squeeze out excess moisture from the thawed spinach. In a mixing bowl, combine spinach with the egg, ricotta, mozzarella, Parmesan, salt, and pepper. Stir until creamy.

Preheat oven to 350°F (175°C). Spread marinara sauce on the bottom of a baking dish. On each noodle, spoon 2-3 tablespoons of filling, roll up, and place seam side down in the dish.

Pour remaining marinara sauce over roll ups, sprinkle with reserved mozzarella. Optionally cover with foil and bake for 30 minutes, then uncover and bake for an additional 5-10 minutes until bubbly.