Heat one tablespoon of the olive oil over medium-high heat in a medium saucepan and add the couscous. Stir until the couscous begins to color and smell toasty, 4 to 5 minutes. Add 2 cups water and salt to taste and bring to a boil. Reduce the heat, cover and simmer 15 minutes, or until the couscous is tender. Drain if any liquid remains in the pan. Transfer the couscous to a large bowl and toss with the lemon juice, parsley, mint, tomatoes, cucumbers, scallions or chives and salt to taste. Add the olive oil, toss together, taste and adjust seasonings. Serve with lettuce leaves.