How to Make It
Preheat the oven to 425°. Using a sharp knife, carefully peel the limes; be sure to remove all of the bitter white pith. Working over a bowl, cut in between the membranes to release the lime sections into the bowl. Cut each section crosswise into quarters. Return the limes to the bowl and stir in the onion, cilantro and jalapeño. Add 1 tablespoon of the oil, the sugar and a pinch of salt and toss well.
Heat the remaining 1 tablespoon of oil in an ovenproof skillet until shimmering. Season the fillets on both sides with salt and pepper and add to the skillet, skinned side up. Cook over moderately high heat until golden brown on the bottom, about 2 minutes. Transfer the skillet to the oven and roast the salmon for 5 minutes, or until just cooked through. Transfer to 4 dinner plates, spoon the salsa on top and serve.