Heat olive oil in a skillet over medium-high heat. Cook and stir onion and garlic in hot oil until onion is tender. Stir in bell pepper and cook until tender but firm. Season with cumin, mustard, cayenne pepper, salt, and black pepper.

Stir kidney beans with liquid and corn with liquid into the skillet. Bring to a boil, reduce heat to medium, and continue cooking, stirring occasionally, until heated through and beans are softened, about 20 minutes.