HEAT oven to 425ºF
COOK chicken in large nonstick skillet on medium heat until lightly browned, stirring frequently. Add 1-1/4 cups milk, Vegetables and Seasoning Mix; stir. Bring to boil; cook 1 min. Simmer on medium-low heat 5 min., stirring frequently. Stir in corn. Spoon into 2-qt. casserole sprayed with cooking spray; cover with Cheese Sauce.
ADD remaining milk to Biscuit Mix; stir just until blended. Spoon over cheese sauce.
BAKE 16 to 18 min. or until filling is heated through and topping is golden brown.