Bring vinegar to a boil in small saucepan. Reduce heat; simmer 6 to 8 minutes or until reduced by half. Set aside.
Press 2 teaspoons garlic-pepper seasoning evenly onto beef Strip Steaks.
Soak four 10-inch bamboo skewers in water 10 minutes; drain. Thread onion wedges onto skewers. Brush onions and cut sides of squash with oil; sprinkle with remaining 2 teaspoons garlic-pepper seasoning.
Place steaks on grid over medium, ash-covered coals; arrange vegetables around steaks. Grill steaks, covered, 11 to 14 minutes (over medium heat on preheated gas grill, 11 to 15 minutes) for medium rare (145°F) to medium doneness (160°F), turning occasionally. Grill squash 8 to 12 minutes (7 to 11 minutes on gas grill) and onions 12 to 15 minutes (13 to 16 minutes on gas grill) or until tender, turning occasionally.
Remove onions from skewers; toss 1/2 of onions with 2 tablespoons reduced vinegar, oregano and salt, as desired. Carve 2 steaks into slices. Serve with onion mixture and 1/2 of squash; season steak and squash with salt, as desired. Cover and refrigerate remaining 2 steaks, onions, squash and reduced vinegar to use in Grilled Beef and Onion Salad.
Nutrition information per serving: 225 Calories; 90 kcal Calories from fat; 10 g Total Fat; 3 g Saturated Fat; 5 g Monounsaturated Fat; 56 mg Cholesterol; 271 mg Sodium; 7 g Total Carbohydrate; 2 g Dietary Fiber; 26 g Protein; 2.1 mg Iron; 7.6 mg NE Niacin; 0.8 mg Vitamin B6; 1.4 mcg Vitamin B12; 4.9 mg Zinc; 29.2 mcg Selenium;