In a large bowl, combine soy sauce, water, sugar, Worcestershire sauce, onion flakes, olive oil, vinegar, and garlic powder.
Stir together until the sugar dissolves. Add chicken breasts; cover and refrigerate for at least 2 hours.
Preheat grill to medium-heat. Using tongs, place chicken breasts on the grill. Cover and cook for 5-7 minutes. Turn breasts over and grill 5-7 minutes longer or until a thermometer reads 165°F.
Notes
Note: Reserve half of grilled chicken for Asian grilled chicken salad recipe.