Preheat oven to 450°F. Melt butter in large ovenproof nonstick skillet on medium-high heat. Add onion; cook and stir 5 minutes or until softened. Sprinkle with flour. Stir with whisk until mixture is well blended. Add stock, milk, apple cider, garlic powder, cinnamon, thyme and pepper; whisk until mixture is smooth.
Stir in chicken, sweet potatoes and peas. Bring to boil. Reduce heat to medium; cook and stir 15 minutes or until sweet potatoes are tender.
Place biscuits on top of chicken mixture. Bake 10 minutes or until biscuits are golden brown.