Preheat oven to 400 degrees. In a medium bowl, whisk together ricotta cheese, eggs, 1/2 teaspoon salt, and 1/4 teaspoon pepper. Add spinach, and stir well to combine.
Spread a small bit of tomato sauce in the bottom of a 9-by-13-inch glass baking dish or dishes. Arrange a layer of lasagna noodles on top. Spread 1/3 of the ricotta mixture over the noodles, followed by 1/3 of the remaining sauce; sprinkle with 1/3 of the grated cheese. Repeat to make two more layers, ending with cheese. If freezing, cover tightly with plastic wrap. Before baking, defrost in the refrigerator overnight.
Cover with aluminum foil. Bake 30 minutes. Remove foil; continue baking until top is golden brown, about 15 minutes more. Let cool slightly before serving.