BRING water to boil in large saucepan on medium-high heat. Stir in macaroni. Reduce heat to medium. Simmer 8 to 10 minutes or until macaroni is tender. Do not drain.
ADD VELVEETA, tuna, corn and seasonings; cook until VELVEETA is completely melted and mixture is heated through, stirring occasionally.
STIR in tomatoes and green onions.