Brown 1 pound of extra-lean ground beef for about 5-7 minutes, stirring occasionally until it's browned and no pink remains. Drain excess fat and set aside.

Stir in one chopped yellow onion and two minced garlic cloves in the same pan, seasoning with salt and pepper. Cook for 3-4 minutes until the onion is translucent. Add in one jar of tomato sauce and let simmer for 5 minutes.

Grease the slow cooker. Layer meat sauce, uncooked lasagna noodles (broken if necessary), ricotta cheese, and mozzarella cheese until full, usually about three layers.

Pour the second jar of tomato sauce over the top layer and add more shredded mozzarella. Pour about a cup of water around the edges. Cover and cook on high for 3 hours or low for 6 hours until bubbly and noodles are tender.

Let the lasagna rest for a few minutes, garnish with fresh basil or parsley, slice, and enjoy.