Preheat the oven to 375°F.
Cook your lasagna noodles according to box directions. Unless you are using oven-ready then you do not need to boil them.
While noodles cook, in a mixing bowl add in ricotta cheese and one egg. Whisk the ricotta and egg together until fully combined and smooth.
(optional) In a frying pan cook down the frozen spinach for 5-10 minutes and season with salt and pepper. Transfer spinach to Ricotta mixture and mix thoroughly.
Drain lasagna noodles once cooked and set aside with a drizzle of oil to prevent sticking.
For assembly you will need 9x13 pan with meat sauce, spinach ricotta mixture, drained noodles, and shredded mozzarella cheese.
Start assembly with small layer of meat sauce. Place layer of lasagna noodles on top. You will likely need 4-5 noodles per layer, depending on pan.
On top of lasagna layer ⅓ ricotta mixture, ⅓ meat sauce, ½ cup mozzarella cheese then place lasagna noodles on top.
Continue this layering process until you finish noodles and finish with remaining meat sauce, ricotta layer, and remaining generous amount of mozzarella cheese.
Cover the pan with aluminum foil and bake in oven for 45 minutes. Then remove aluminum foil and bake for 10 more minutes. Broil on HIGH for 3 minutes until mozzarella is golden and bubbling.
Let it sit for 10 minutes before serving.
Enjoy!