Method:
Soak the chile peppers in enough warm water to cover them for 30 minutes, until soft. When the chiles are soft, remove and discard the stems and seeds, then transfer to blender. (Reserve soaking liquid.) Add sugar, lime juice, garlic, oregano and salt and purée until you have a paste-like consistency. If the mixture is too thick, add a little of the chile soaking liquid, 1 teaspoon at a time, until the desired consistency is reached.
Preheat the oven to 350°F. Arrange salmon fillets on a parchment paper-lined baking sheet skin side down, just touching, so they resemble a whole side of salmon. Spread the chile purée evenly over the tops of the salmon to completely cover each fillet.
Lay lime slices down the center of the salmon in one straight line, then brush them with oil. Bake for 25 to 30 minutes, until salmon is golden brown and fully cooked through. Carefully remove the salmon fillets to a serving platter, recreating the original shape. Serve hot from the oven, at room temperature or chilled. Garnish with cilantro.