Place beef steaks and 1/4 cup dressing in food-safe plastic bag; turn steaks to coat. Close bag securely and marinate in refrigerator 30 minutes to 2 hours.
Remove steaks from marinade; discard marinade. Place steaks on grid over medium, ash-covered coals; arrange potatoes and squash around steaks. Grill beef, covered, 11 to 13 minutes (over medium heat on preheated gas grill, 13 to 15 minutes) for medium rare (145°F) doneness, turning occassionally. (Do not overcook steak.) Grill potatoes 13 to 15 minutes (gas grill times remain the same) and squash 7 to 10 minutes (gas grill times remain the same) or until vegetables are tender and lightly browned, turning occasionally and brushing with 2 tablespoons dressing.
Carve steak into thin slices; season with salt, as desired. Cut potatoes and squash into 1-inch pieces. Combine lettuce and vegetables in large bowl. Combine lettuce mixture with remaining dressing; toss evenly to coat. Divide lettuce mixture evenly among four plates. Top with steak slices.
Nutrition information per serving: 359 Calories; 81 kcal Calories from fat; 9 g Total Fat; 3 g Saturated Fat; 3 g Monounsaturated Fat; 65 mg Cholesterol; 723 mg Sodium; 48 g Total Carbohydrate; 5.2 g Dietary Fiber; 29 g Protein; 4.8 mg Iron; 10.2 mg Niacin; 1.1 mg Vitamin B6; 2.8 mcg Vitamin B12; 6.7 mg Zinc; 34.2 mcg Selenium; 120.4 mg Choline;