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Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce.
Zest and quarter one lime; halve the other lime (for 4 servings, zest and quarter two limes; halve the remaining two).
Trim scallions; thinly slice whites crosswise. Halve greens lengthwise (making sure not to cut all the way through), then open like a book. Lay flat, then slice lengthwise into very thin strips. Soak in a bowl of ice water until they curl; drain and pat dry with paper towels.
Peel and mince or grate ginger. Peel and mince or grate garlic. Halve, peel, and finely dice onion.