Heat oil in a large skillet; add onions, garlic, and mushrooms. Saute until soft. Add tomatoes, green pepper, celery, and oregano.

Cover skillet and simmer for about 5 minutes or until vegetables are crisp-tender. Add beans and simmer, stirring occasionally, until heated through. Add salt and pepper to taste.

Spoon beans and veggies over rice, top with cheese, sour cream, hot sauce, etc.