MIX flour, cereal and salt in large bowl. Using a pastry blender or 2 knives, cut in 5 Tbsp. of the margarine until mixture forms fine crumbs. Gradually add 4 Tbsp. of the water, stirring until mixture forms ball. Add remaining 1 Tbsp. water, if necessary for ball to stick together.
ROLL pastry into 11-inch circle on lightly floured surface. Line 9-inch pie plate with pastry, allowing 1/2-inch overhang. Turn under edge; flute. Pierce pastry shell with fork. Bake at 450°F for 7 minutes. Remove from oven. Reduce oven temperature to 375°F.
MELT remaining 1 Tbsp. margarine in large skillet on medium heat. Add potatoes, green pepper, onion and sausage. Cook and stir 3 minutes or until onions are tender. Pour into pastry shell.
BEAT eggs, milk and thyme with wire whisk until well blended. Stir in cheese. Pour into pastry shell; stir gently until well blended.
BAKE 40 to 50 minutes or until knife inserted in center comes out clean.