1 lb. ground beef
1 medium onion, halved and thinly sliced
2 (16 oz.) cans kidney beans, rinsed and drained
1 (14 1/2 oz.) can diced tomatoes (undrained)
1/2 to 3/4 c. water
1 tbsp. chili powder
1 tbsp. vinegar
2 tsp. prepared mustard
1 tsp. salt
1/8 tsp. pepper

Brown beef and onion and drain. Add beans, tomatoes, water, chili powder, vinegar, mustard, salt and pepper. Bring to boil; reduce heat. Cover and simmer for 10 minutes or until heated through. Serve.

I sometimes cook much longer, adding more water as needed.