Slow Cooker Lasagna

1 Lb ground beef cooked and drained
1 small onion, chopped, cooked with ground beef
1 26oz jar, or fresh spaghetti sauce
1 16oz ricotta cheese (light is fine)
8 oz mozzarella cheese
1/4 cup parmesan cheese, divided
1 egg
2 Tbsp parsly
6 lasagna noodles, uncooked

After beef and onion is browned, add sauce. In a separate bowl, combine ricotta, 1 1/2 cup mozzarella, 2 Tbsp parmesan, egg and parsley. Spoon 1 cup of meat sauce on bottom of cooker and layer. Start with noodles and end with sauce and remaining cheese. If during the cooking process it looks dry, sprinkle with some water.
**When I use lasagna noodles in other recipes and I have any leftover, I freeze them in baggies and use them for this recipe. Doesn't taste any different. Just being frugal.