Prepare Tiger Grouper Fillet by slicing it into smaller pieces of 100-150g portions. Preheat oven to hot.
Heat oil in a large ovenproof skillet over medium-high heat. Carefully place fillets, top side down, in hot oil. Cook 3 to 4 minutes or until the edges are lightly browned.
Transfer the skillet to oven and continue baking at a high temperature for 4-5 minutes until the fish is fully cooked. Once cooked place fish on a plate skin side down.
Pour butter into a small bowl. Whisk in vinegar, shallot, and squeeze in the lemon slice. Pour this over the tiger grouper fillet. Season with salt and pepper.