Combine Ground Beef, bread crumbs, egg white and seasoned salt in medium bowl, mixing lightly but thoroughly. Lightly shape into four 1/2-inch thick patties. Brush onion slices with 1/2 tablespoon oil.
Place patties and onion slices on grid over medium, ash-covered coals. Grill patties, covered, 8 to 10 minutes (over medium heat on preheated gas grill 7 to 9 minutes), until instant-read thermometer inserted horizontally into center registers 160°F, turning occasionally. Grill onions, 11 to 13 minutes or until tender, brushing with remaining 1/2 tablespoon oil and turning occasionally.
Line bottom of each bun with lettuce. Place tomatoes and burgers on lettuce. Spoon dressing over burgers; top with onions. Close sandwiches.
Nutrition information per serving: 339 Calories; 108 kcal Calories from fat; 12 g Total Fat; 3 g Saturated Fat; 2 g Monounsaturated Fat; 67 mg Cholesterol; 862 mg Sodium; 32 g Total Carbohydrate; 4.5 g Dietary Fiber; 28 g Protein; 4 mg Iron; 8.3 mg Niacin; 0.5 mg Vitamin B6; 2.1 mcg Vitamin B12; 6.3 mg Zinc; 41.8 mcg Selenium; 95.5 mg Choline;