Finely chop the onion. In a skillet, heat 1 tablespoon olive oil. Add the onion and green pepper and saute until soft, about 4 to 5 minutes.
If using canned beans, drain the beans and rinse. Add the remainder of the ingredients above (starting with kidney beans) to the skillet, and simmer for about 5 to 10 minutes. Taste, and adjust seasoning as desired.