PREHEAT oven to 400°F. Mix milk, dressing and flour in large microwaveable bowl. Microwave on HIGH 2 to 3 min. or until sauce is thickened, stirring after each min. Add turkey, mixed vegetables, cheese and onions; toss to coat. Spoon into 9-inch pie plate; smooth surface.
PLACE crust over filling; flute edge of crust, sealing edge of crust to rim of pie plate. Cut several slits in crust to allow steam to escape. Transfer to baking sheet.
BAKE 30 min. or until golden brown.