Cook the noodles - Boil lasagna noodles until al dente. Lay flat on clean kitchen towels.
Make the meat - Brown sausage in a large pan, breaking it into small pieces. Add onion and cook until soft. Add garlic and cook 1 more minute. Season with red pepper flakes if using.
Mix the cheese - Combine ricotta, 2 cups mozzarella, parmesan, eggs, and parsley in a large bowl. Season well with salt and pepper.
Assemble - Spread cheese mixture on each noodle, add sausage mixture. Roll up from one end.
Bake - Put a little sauce in bottom of 9x13 pan. Place rolls seam-side down. Cover with remaining sauce and extra mozzarella. Cover with foil and bake at 350°F for 30 minutes.
Finish - Remove foil and broil 2-3 minutes until cheese is brown and bubbly.