Step 1Combine onion, rice vinegar, water, ginger, celery, ketchup, soy sauce, sugar, lemon juice, garlic, salt and pepper in blender on high speed. Add oil in small stream and mix until blended. Chill at least 10 minutes. (Makes 1 3/4 cups.)
Step 2To serve, divide lettuce among 4 serving bowls and toss each with 2 tablespoons dressing.