Preheat oven to 375 degrees F.
Over medium-high heat, boil water in a large pot. When boiling, add lasagna noodles and cook as directed on the package.
In a medium-sized bowl, mix ricotta, egg whites, garlic and parsley. Season with salt and pepper as needed.
When noodles are done cooking, cool them down to room temperature by rinsing them continuously with cold water and letting them sit in cold water until ready to use.
In a lasagna tray or casserole dish (whatever dish you'd like to cook the lasagna in), start with a thin layer of marinara sauce, followed by a layer of lasagna noodles, the ricotta mixture, and then a healthy amount of baby spinach. Don't worry about the spinach being too much - it packs back down when you add the next set of layers! Repeat that layering about 3-4 more times, depending on how high you want your lasagna to be. Top the lasagna off by covering the entire dish with mozzarella cheese slices.
Cover lasagna with tin foil.
Place lasagna in oven and cook for ~ 30 minutes. After, remove the tin foil, and continue to cook for about another 15-20 minutes or until the cheese is fully melted and starting to bake.
Let cool outside of the oven for about 10 minutes, slice and serve!