In a large mixing bowl, combine the ricotta cheese, egg, minced garlic, oregano, basil, salt, and pepper. Mix well until smooth and set aside.
Cook the lasagna noodles according to the package instructions until al dente. Drain and lay them flat on a clean kitchen towel.
In a large mixing bowl, mix the shredded chicken with the spinach and half of the mozzarella cheese. Set aside.
In a greased 9x13 inch baking dish, start layering your lasagna: Spread 1 cup of marinara sauce on the bottom of the dish. Place 4 lasagna noodles on top, overlapping slightly. Spread half of the ricotta mixture over the noodles, then half of the chicken and spinach mixture. Sprinkle 1/3 of the remaining mozzarella cheese. Repeat the layering process: another cup of marinara sauce, 4 lasagna noodles, the other half of the ricotta mixture, the other half of the chicken-spinach mixture, and another 1/3 of the mozzarella. Top with the last 4 lasagna noodles, the remaining marinara sauce, and finish with the rest of the mozzarella and the grated Parmesan cheese on top.
Cover the baking dish with aluminum foil (avoid touching the cheese) and bake in the preheated oven for 30 minutes.
Remove the foil and bake for an additional 15-20 minutes, or until the cheese is bubbly and golden.
Remove from the oven and let it cool for about 10-15 minutes before slicing.
Garnish with fresh basil leaves if desired before serving.
Notes
Let the lasagna cool for a few minutes before slicing for easier serving.