COOK spaghetti in large saucepan according to pkg. directions, adding the spinach, peppers and mushrooms to the water for the last 3 min. of the spaghetti cooking time. Place spaghetti mixture in colander; drain.

MEANWHILE, add cream cheese and milk to same saucepan; cook on low heat until cream cheese is completely melted and mixture is well blended, stirring frequently.

PLACE spaghetti in large bowl. Add cream cheese mixture; toss to coat. Sprinkle with the grated cheese.