1 Score meat in a diamond pattern on both sides, cutting about 1/4 inch deep. Place meat in a large plastic bag set in a shallow dish. In a small mixing bowl combine wine vinegar, onion, oil, Worcestershire sauce, the 2 cloves garlic, and the dry mustard. Pour over meat. Seal the bag; turn to coat. Marinate in the refrigerator for 6 to 24 hours, turning the bag occasionally.
2 For sauce, in a medium saucepan cook the green onions in 2 tablespoons of the margarine or butter until tender. Stir in the flour and dried thyme. Stir in broth and wine. Bring to a boil, stirring occasionally; reduce heat. Boil gently, uncovered, for 15 to 20 minutes or until reduced to 1 cup. Keep warm.
3 Meanwhile, remove steak from marinade; pat dry with paper towels. Place steak on unheated rack of a broiler pan. Discard marinade. Broil steak 3 to 4 inches from the heat for 13 to 15 minutes (for medium-rare), turning steak halfway through cooking time. Slice flank steak thinly across the grain.
4 Meanwhile, combine zucchini, carrot, and the 1 clove garlic; place in a steamer basket over boiling water. Steam for 3 to 4 minutes or just until tender. Stir in the remaining margarine or butter and the walnuts. Season to taste with salt and pepper.