Step 1In a small pan, melt the butter over medium heat. Add the garlic and cook until lightly browned. Add the lime juice and zest and remove from the heat. Add the salt and pepper. Let cool to warm and then add the cilantro. Set aside.
Step 1Scrape the dull side of a knife against the skin of the fish from tail to head to remove fine scales and excess moisture. Cut 3 or 4 diagonal slashes down to the bone on each side. In a bowl, mix together the cumin, garlic, ginger, salt, sugar, lemon zest and cilantro. Season the fish inside and out with the mixture. Rub 2 tablespoons of olive oil over the fish.
Step 2Put the fish on a liberally oiled grill (alternately, you can use a well-oiled grill screen or fish basket). Cover and cook over medium heat until browned on both sides and an instant-read thermometer reads 130 degrees, about 12 to 15 minutes. Serve with the warm lime-cilantro butter sauce.