BROWN meat in large nonstick skillet on medium-high heat; drain. Return to skillet.
STIR in Macaroni, Cheese Sauce Mix, tomatoes, peas and milk. Bring to boil; cover. Simmer on medium-low heat 12 min. or until macaroni is tender, stirring occasionally.
TOP with mozzarella. Remove from heat. Let stand, covered, 5 min. or until mozzarella is melted.