kidney bean cabbage soup

1 medium yellow onion, chopped
1 15oz can white kidney beans, rinsed and drained
1 25oz can red kidney beans, rinsed and drained
8-10oz mushrooms, sliced
1/2 head cabbage, chopped
2-3T olive oil
1tsp dried oregano
1qt vegetable broth

Saute onion and oregano in oil until onion starts to become clear. Add mushrooms and saute 1-2 minutes further. Add broth and both colors of beans and bring to a boil. Add cabbage and cook 5 minutes, stirring frequently. Serve hot.