Slow Cooker Lasagna

pound(s) uncooked 93% lean ground beef

small uncooked onion(s) chopped

clove(s), medium garlic clove(s) minced

canned crushed tomatoes

canned tomato sauce

table salt

dried oregano

dried basil

crushed red pepper flakes or to taste

cup(s) part-skim ricotta cheese

cup(s) shredded part-skim mozzarella cheese divided

item(s) uncooked lasagna noodles

cup(s) shredded parmesan cheese strong-flavored like Parmigiano Reggiano