Grouper is healthiest when it is baked in the oven. Arrange your fish fillets or steaks in a single layer and add a light touch of olive oil before you put it in the oven to keep it from drying out. The time and temperature to bake grouper can vary, but to get the best results you should set your oven to 400 degrees Fahrenheit and cook it for 12 to 15 minutes. Your fish must be baked to an internal temperature of 145 degrees Fahrenheit in order to be considered safe for consumption; if you don’t have a thermometer on hand, you can tell your grouper is done when the meat is opaque and flakes easily with a fork.