Prepare noodles according to package directions; drain and set aside. Saute Italian sausage, onion and garlic in a skillet until sausage is browened; drain. Add pasta sauce to the sausage mixture and set aside. In a medium bowl, blend ricotta cheese, egg and 1/4 cup of Parmesan cheese and set aside.
Coat a 9x13 baking dish with non-stick spray and spread 1 cup of the sauce mixture on the bottom. Top with 3 lasagna noodles. Spread 1/4 cup of the ricotta cheese mixture on the noodles and layer on 1 cup of the sauce mixture. Sprinkle 1 cup of the spinach and 1/2 cup mozzarella cheese. Repeat thi whole process 3 more times starting with the noodles, top with 1/4 cup Parmesan cheese to finish.
Bake uncovered in a 350 degree oven for 45 minutes until hot and bubbly. Let stand 10 minutes before cutting.