Cook the lasagna noodles according to package instructions; drain and set aside.
In a bowl, mix together the spinach, ricotta cheese, 1/2 cup mozzarella cheese, Parmesan cheese, egg, garlic powder, Italian seasoning, salt, and pepper.
Spread a thin layer of marinara sauce on the bottom of a baking dish.
Take a lasagna noodle and spread a portion of the spinach mixture on it, then roll it up tightly.
Place the rolled noodle seam-side down in the baking dish.
Repeat with the remaining noodles and filling.
Pour the remaining marinara sauce over the rolled noodles and sprinkle with the remaining mozzarella cheese.
Cover with foil and bake for 25 minutes.
Remove the foil and bake for an additional 10 minutes, or until the cheese is bubbly and golden.
Notes
Feel free to add other vegetables like mushrooms or zucchini to the filling.
This dish can be made ahead of time and stored in the refrigerator before baking.
For a vegan version, substitute ricotta and mozzarella with plant-based alternatives.