Melt margarine in 3-quart saucepan over medium heat and cook green onions, stirring occasionally, 3 minutes or until tender. Add water and bring to a boil. Stir in Knorr® Pasta Sides™ - Chicken flavor and vegetables, then continue boiling over medium heat, stirring occasionally, 7 minutes or until pasta is almost tender. Stir in cheese, mustard and milk blended with flour. Cook over medium heat, stirring frequently, 2 minutes or until thickened.
Turn into greased 1-quart round casserole or souffle dish, then top with pastry. Press pastry around edge of casserole to seal; trim excess pastry, then flute edges. (Use extra pastry to make decorative shapes.) Brush pastry with egg yolk mixture. With tip of knife, make small slits in pastry. Bake 12 minutes or until crust is golden brown.