Place steak in large plastic bag with mixture of 2 Tbsp. lite soy sauce, 1 Tbsp. vinegar, garlic and pepper. Press air out of bag; close top securely. Turn bag over several times to coat both sides. Marinate 30 minutes; turn bag over once. Meanwhile, combine remaining lite soy sauce, vinegar, oil and oregano; set aside. Broil steak 4 minutes on each side (for rare), or to desired doneness; cut across grain into thin slices. Combine with remaining 3 ingredients in large bowl. Blend soy sauce mixture; pour over spinach mixture and toss to combine. Makes 4 to 6 servings.