Heat oven to 350°F. In small bowl, mix cream cheese, mustard and chives; blend well. Spread on cut sides of bagels. Place on ungreased cookie sheet.
Core apple; cut into 1/2-inch-thick rings. Place 1 apple ring on each bagel half; top each with piece of cheese.
Bake 5 to 6 minutes or until cheese is melted and sandwiches are warm.