In a large skillet over medium-high heat, cook ground beef, onion, green pepper, and garlic until beef is cooked through and vegetables are softened, about 5 minutes. Drain excess fat.
Add spaghetti sauce, Italian seasoning, sugar, salt and pepper. Simmer for 10 minutes.
Spread 1/3 of the meat sauce in the bottom of a 6-quart slow cooker.
Top with 3 lasagna noodles, breaking them to fit if necessary.
Top with half of the remaining sauce, 1 cup mozzarella cheese, and 1/4 cup Parmesan cheese.
Repeat layering with 3 noodles, remaining sauce, 1 cup mozzarella cheese, and 1/4 cup Parmesan cheese.
Finish with remaining 3 noodles, 1 cup mozzarella cheese, and 1/4 cup Parmesan cheese.
Cover and cook on low for 4-5 hours, or until noodles are tender.
Let stand for 10 minutes before serving.
Interesting Facts
Lasagna is a traditional Italian dish that consists of layers of pasta, cheese, and sauce.
Lasagna can be made with either meat or vegetables.
Lasagna is usually baked in the oven, but can also be cooked in the slow cooker.
Lasagna is a great dish to make ahead and freeze for later.