Remove sausage from casings and mix with ground beef. Cook the meat with onions and peppers in a large skillet until meat is lightly browned, about 10-15 minutes. Add garlic during last 5 minutes of cooking. Drain excess fat. Mix cooked meat mixture with marinara sauce.

Spoon a small amount of sauce in bottom of slow cooker to cover. Follow this with a layer of uncooked lasagna noodles (break noodles to fit the round contours of most slow cookers, don't worry if they overlap and aren't perfect). Top noodles with a layer of sauce. Follow this with a thin layer of the ricotta or cottage cheese then sprinkle with Parmesan and mozzarella. Continue layering until you reach the top of the slow cooker (or you run out of ingredients), finishing with a layer of cheese. Cook on low 6 to 8 hours.

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