Thoroughly blend oil and lite soy sauce; remove and reserve 1/4 cup. Pour remaining mixture over onion and parsley in small bowl; stir to coat all pieces well. Let stand 15 minutes, stirring occasionally.
Meanwhile, cut bread into 12 slices, each 1/2 inch thick. Lightly brush both sides of bread with reserved soy sauce mixture; place on large baking sheet.
Broil 1 to 2 minutes on each side, or until golden. Drain onion mixture; set aside. Cover each bread slice with roast beef and then onion mixture. Sprinkle cheese evenly over onion mixture; serve immediately.