In a large skillet over medium heat, cook the ground beef with diced onion until browned and the onion is soft, about 5-7 minutes. Drain any excess fat.

Stir in minced garlic, marinara sauce, tomato sauce, dried basil, dried oregano, salt, and black pepper. Bring to a simmer and cook for 2-3 minutes, then remove from heat.

In a medium bowl, mix ricotta cheese with grated Parmesan. Set aside.

Spray the crockpot insert with cooking spray to prevent sticking.

Spread 1 cup of the meat sauce on the bottom of the crockpot.

Place a layer of uncooked lasagna noodles over the sauce, breaking them to fit if needed.

Dollop and gently spread about ⅓ of the ricotta mixture over the noodles, then sprinkle with ½ cup mozzarella.

Repeat layers (meat sauce, noodles, ricotta, mozzarella) two more times, ending with a final layer of noodles, sauce, and mozzarella on top.

Cover and cook on LOW for 4-5 hours, or until noodles are tender and lasagna is bubbling.