HEAT oven to 375ºF. Mix soup and 1/2 cup sour cream in 8-inch square baking dish. Stir in chicken, vegetables and cheese.
STIR milk and remaining sour cream into baking mix. Drop by heaping tablespoonfuls into 6 mounds on top of chicken mixture.
BAKE 35 min. or until biscuit topping is golden brown and chicken mixture is hot and bubbly.