Tomato-Watermelon Salad

5 cups seeded watermelon, cut into small cubes
1 ½ lbs. ripe tomatoes, cut into cubes
3 tsp. sugar
½ tsp. salt
1 small red onion, quartered and thinly sliced
½ cup red wine vinegar
¼ cup extra virgin olive oil
Romaine lettuce leaves (optional)
Cracked black pepper to taste

Combine watermelon and tomatoes in a large bowl; sprinkle with sugar and salt, tossing to coat. Let stand 15 minutes. Stir in onion, vinegar, and oil. Cover and chill 2 hours. Serve chilled with lettuce leaves, if desired. Sprinkle with cracked black pepper to taste.

(from Southern Living Magazine)