Fresh spinach adds a healthy dose of fiber to this simple lasagna recipe. Slideshow: More Easy Lasagna Recipes
Preheat oven to 375°. Lightly coat a 2-quart baking dish with olive oil and set aside.
Cook lasagna noodles until al dente according to package instructions. Rinse under cold water until cool. Lay the cooked pasta flat and set aside.
In a medium bowl, combine the ricotta cheese, egg, Parmigiano-Reggiano, lemon zest, salt and pepper. Set aside.
Spread a light layer of tomato sauce on the bottom of the baking dish. Lay 3 to 4 lasagna noodles lengthwise over the sauce.
Layer one-third of the remaining tomato sauce over the lasagna noodles and then layer half of the ricotta mixture. Layer half of the spinach over the ricotta and then spread one-third of the mozzarella cheese. Repeat this pattern: noodles, sauce, ricotta cheese, spinach and mozzarella cheese. Add a final layer of lasagna noodles and then add the remaining tomato sauce and remaining mozzarella cheese.
Bake lasagna for about 45 minutes or until the top cheese is melted and golden.
Remove from oven; let cool for about 10 to 15 minutes before serving.