Brown the ground beef or sausage in a skillet over medium heat.
Drain excess fat and add marinara sauce to the meat. Simmer for 5 minutes.
In a bowl, mix ricotta cheese, egg, Italian seasoning, salt, and pepper.
Spray the crockpot with cooking spray.
Spread a thin layer of meat sauce at the bottom of the crockpot.
Place 3 lasagna noodles over the sauce, breaking them if necessary.
Spread half of the ricotta mixture over the noodles.
Add a layer of meat sauce, followed by a layer of mozzarella cheese.
Repeat the layering process until ingredients are used, finishing with mozzarella on top.
Cover and cook on low for 4-6 hours or high for 2-3 hours.