Heat oil in a medium saucepan over medium heat. Add bell pepper, onions, and garlic and sauté 2 minutes or until softened. Add beans, stock, coriander, and cumin. Bring to boil, reduce heat, and simmer 5 minutes.
Transfer half the soup to a food processor or blender, cover, and purée until smooth. Return to pan and cook until heated through. Ladle into bowls and top each serving with sour cream and tomato.