Preheat oven or grill to 400° F. Place salmon on a foil-lined baking sheet, skin side down (this will make cleanup easier). Do not grease the foil.
Squeeze lemon over salmon filet. Sprinkle garlic and cilantro evenly over the top. Sprinkle with salt and pepper. If using, thinly slice butter and place pieces evenly over the top of the salmon.
Place foil with salmon on the preheated grill, or bake salmon in preheated oven about 7 minutes, depending on thickness. (If you are grilling, skip the next step and continue to grill for a total of about 15 minutes.)
Turn oven up to broil and continue to cook an additional 5-7 minutes, until the top is crispy.
Remove salmon from oven or grill and slide a flat spatula in between the salmon and the skin. The skin should stick to the foil, making separation of the fish from the skin easy. Serve immediately.