Combine sour cream and cream cheese in a large bowl, stirring until smooth. Stir in taco seasoning.
Add beans, stirring until well blended. Spoon mixture into an 11 x 7-inch baking dish coated with cooking spray.
Bake at 350 for 10 minutes; sprinkle with cheese, and bake an additional 10 minutes or until cheese melts and dip is bubbly. Top with tomato and green onions.