To make pan-seared grouper, season the fillets with salt and pepper, place in a hot pan with oil and cook on both sides until fully cooked. Enjoy the fillets as is, or top them with a simple butter sauce.
To sear the grouper well, use paper towels to pat the fillets dry and ensure there is no excess water on the surface of the fish. Too much moisture prevents a good sear. Season both sides of the fillets and set aside. Place the skillet over high heat until it's very hot before adding about 2 tablespoons of oil. Use oil that can withstand high heat, such as canola oil. Swirl the oil around to fully coat the pan.
Once the pan and oil are hot, lay the grouper fillets down in the pan. If the fillets have skin, lay them skin-side-down in the pan first. Shake the pan slightly to ensure that the fish doesn't stick. Gently press down on the fish with a spatula for an even sear. Flip the fish over after about three to four minutes. Cook on the other side for a few minute more until the flesh is opaque and flakes easily with a fork.
To make a simple lemon butter sauce for the grouper, combine 3 tablespoons of melted butter with 2 teaspoons of lemon juice and pour over the fish.