1
Adjust rack to top position and preheat oven to 450 degrees. Wash and dry produce.
Halve, peel, and thinly slice half the onion (all for 4 servings). Zest and quarter lime. Finely chop cilantro. Trim and discard root end from lettuce; thinly slice leaves crosswise into strips until you have 4 cups (8 cups for 4); halve strips crosswise. Dice tomato into ½-inch pieces.