In a soup pot, heat 2 tablespoons oil over medium heat. Add onion and cook, stirring often, till onions are soft, about 3 minutes. Add cabbage, garlic and oregano; cook, stirring often till the cabbage has wilted, about 3 minutes. Add broth, mashed beans, and whole beans; bring to a boil. Reduce heat to medium-low and partially cover, simmering till cabbage is soft, 10 to 12 minutes. Season with salt and pepper.