Gather all your ingredients to streamline the cooking process.
In a large skillet over medium heat, brown the ground beef with the diced onion and minced garlic for 5-7 minutes. Drain excess fat.
Transfer the cooked beef mixture to the Crock-Pot. Add crushed tomatoes, tomato sauce, and beef broth. Stir in dried basil, oregano, red pepper flakes, salt, and pepper.
Cover and cook on low for 6-8 hours or on high for 3-4 hours.
About 30 minutes before serving, stir in the broken lasagna noodles. Cover and let cook until tender. Mix in ricotta and half of the mozzarella cheese before serving.
Serve hot, topped with remaining mozzarella and Parmesan cheese, and garnish with fresh herbs if desired.