1In 3-quart saucepan, heat water, butter and salt to boiling; remove from heat. Stir in milk and dry potatoes just until moistened. Let stand about 30 seconds or until liquid is absorbed; whip with fork.
2In 1-quart saucepan, cook beans and tomatoes over medium heat 8 to 10 minutes, stirring occasionally, until hot. Spoon onto individual servings of potatoes. Sprinkle with cheese and onions.