Greek-Style Salad

3 tablespoons fresh lemon juice
1 teaspoon sugar
1/4 cup extra-virgin olive oil
1 pound beefsteak tomatoes, cut into 1-inch-thick wedges
1/2 medium red onion, thinly sliced crosswise
1 head radicchio (1/2 pound), halved lengthwise, then thinly sliced crosswise
1 head romaine, coarsely chopped (6 cups)
2 small cucumbers, peeled if desired, halved lengthwise, then thinly sliced crosswise
2/3 cup mixed Greek olives (1/4 pound)

Whisk together lemon juice, sugar, 1/2 teaspoon salt, and 1/8 teaspoon pepper in a large bowl until sugar and salt have dissolved.

Add oil and whisk until combined well. Stir in tomatoes and onion and let stand 10 minutes.

Add remaining ingredients and toss to coat.