1.Preheat oven to 220°C. Oil oven tray.
2.In a large frying pan, heat oil; cook onion and garlic, stirring, until onion softens. Add chicken, frozen vegetables, mustard, sour cream and cheese; stir until heated through.
3.Cut one 22cm round from each pastry sheet. Spoon a quarter of the filling in centre of each round. Brush edge of pastry with a little of the egg; fold pastry over to enclose filling, pinching edges together to seal. Place pasties on tray; brush with remaining egg.
4.Bake pasties about 30 minutes or until browned.