Place cooked veggies in 9x13 baking dish. Put cooked chicken on top of veggies.
In saucepan, melt butter. Saute onion. Stir in flour, cooked stock, and cream of celery soup. Pour this mixture over veggies and chicken. Bake in hot 450 degree oven for 15 minutes. Placed canned biscuits or your own recipe biscuits on top and bake at 400 degree oven for 10 minutes or until golden brown.