Preparation / Directions:
Combine the butter, cilantro, lemon or lime juice and zest, salt and pepper in a bowl and beat by hand with a wooden spoon. Shape into a rough log about 2 inches long and 1 inch in diameter, wrap in plastic wrap and chill until firm. Prepare a fire in the grill.
Position the oiled rack 4-6 inches above the fire. Rub the fish lightly with oil and sprinkle to taste with salt and pepper. Arrange the fish on the grill.
Cook, turning once, about 10 minutes; the fish is done when it turns from translucent to opaque throughout.
Remove to a warmed platter or plates. Cut the cilantro butter into 4 equal slices and top each fillet with a slice.