PREHEAT oven 350°F. Mash beans in large bowl. Add cream cheese, sour cream and chilies; mix well. Remove 1/2 cup of the shredded cheese; refrigerate for later use. Stir remaining shredded cheese into bean mixture. Spread into lightly greased 8-inch casserole or baking dish.
BAKE 20 min.; sprinkle with the reserved 1/2 cup shredded cheese. Continue baking 5 min. or until shredded cheese is melted.
SPRINKLE with onions. Serve with Triscuit Thin Crisps Crackers and assorted cut-up vegetables, if desired.