Bring chicken broth to a boil; add carrots, onions, celery, mushrooms and garlic; simmer 10 minutes. Add cubed chicken meat and peas; simmer 5 minutes more. Mix cornstarch with cold water in measuring cup; add slowly until chicken mixture has consistency of gravy. Remove from heat; cool.
To freeze: pour into round casserole dish (2-qt capacity). Cover with aluminum foil; flash freeze, then wrap in jumbo freezer bag.
To prepare: thaw casserole before cooking. Place in 400-degree oven for 25 minutes. Remove from oven and place uncooked biscuits (either from "tube" or scratch--my family enjoys their "chicken biscuits" cut with a chicken-shaped cookie cutter) in slightly-overlapping circles on top of casserole. Return to oven and bake 20 to 25 minutes more, until mixture is bubbling and biscuits are golden brown.