SQUEEZE lemons; STRAIN juice into glass measuring cup.
ADD salt and pepper to juice; WHISK until the salt dissolves; ADD oil; WHISK again until combined; SET aside.
FLAKE the drained tuna; ARRANGE tuna on bed of lettuce with sliced onion, cucumber and tomato.
WHISK dressing until uniform cloudy color; DRIZZLE over salad.
May double dressing recipe and store remainder in refrigerator for later use. Tuna is usually packed in 6 ounce cans--use one can per serving. We prefer water-packed tuna over oil-packed.
Per Serving (excluding unknown items): 393 Calories; 37g Fat (78.8% calories from fat); 4g Protein; 19g Carbohydrate; 4g Dietary Fiber; 0mg Cholesterol; 1089mg Sodium. Exchanges: 2 1/2 Vegetable; 1/2 Fruit; 7 1/2 Fat.