Heat oil in a large stockpot over medium-high heat. Add ground beef and onion; cook and stir until beef is well browned and crumbly and onion is translucent, 5 to 7 minutes. Drain fat.
Transfer beef mixture to a slow cooker. Add cabbage, kidney beans, tomato sauce, water, bouillon, cumin, salt, and pepper; stir to combine.
Cover and cook on Low for 6 to 8 hours or High for 4 hours, stirring occasionally.