Bring a large pot of lightly salted water to a boil.
Add lasagna noodles and cook 8 to 10 minutes until al dente. Drain noodles in a colander.
Place frozen spinach and ½ cup water in a medium nonstick saucepan.
Bring to a boil, then reduce heat to medium-high and cover.
Cook, stirring occasionally, until spinach is tender, 6 to 7 minutes
Drain spinach and squeeze out excess water.
Stir diced chicken and 1 jar Alfredo sauce in a medium bowl.
Mix ricotta and drained spinach in a second medium bowl.
Spread a thin layer of Alfredo sauce from the second jar in a 9x13-inch baking dish.
Arrange a single layer of noodles, edges slightly overlapping.
Spread the chicken-Alfredo mixture evenly over the noodles.
Sprinkle 1 cup mozzarella over the chicken layer. Add a second layer of noodles.
Spread the spinach-ricotta mixture evenly over the noodles.
Pour ½ of the remaining jar of Alfredo sauce over the spinach mixture and spread evenly.
Sprinkle 1 cup mozzarella over the sauce. Add a final layer of noodles.
Top with the remaining ½ jar Alfredo sauce.
Sprinkle the remaining 2 cups mozzarella over the top.
Season the surface lightly with salt and black pepper.
Bake until the top is browned and bubbly, 50 to 60 minutes.
Rest 10 minutes before slicing and serving.
Notes
How to Store and Reheat
Refrigerate - Cool completely, cover, and refrigerate up to 4 days. Store in the baking dish or transfer to airtight containers.Freeze - Wrap tightly and freeze up to 2 months. For best quality, freeze in portions.Reheat in the oven - Cover with foil and reheat at 325°F until hot, about 20 to 30 minutes for a large portion. Remove foil for the last few minutes to refresh the top.Reheat in the microwave - Heat slices on a microwave-safe plate in short bursts, 50% power, stirring any escaping sauce back over the pasta between bursts to keep it moist.