Cook lasagna noodles according to package directions. Preheat oven to 350 degrees.
Squeeze excess liquid out of frozen spinach. In a medium bowl, mix together ricotta, spinach, egg, salt and pepper.
Spread 1 cup of pasta sauce on the bottom of a large casserole dish.
Drain noodles. Take one lasagna noodle at a time and lay it on a flat surface. Spread a layer of the ricotta mixture on the noodle, then roll it up tightly. Set roll in casserole dish seam side down. Repeat until all of the noodles have been rolled and placed in the casserole dish.
Spread the rest of the pasta sauce over the rolls, then sprinkle with mozzarella cheese.
Cover with foil, then bake in the oven for about 35 minutes. Remove foil and bake 5-10 minutes longer, until cheese just begins to brown.