To reheat leftovers, you can heat the fish for 30 seconds in the microwave, then toast it in a toaster oven for 2-3 minutes to crisp up the exterior. If you don't have a toaster oven, you can let the fish come to room temperature, then heat it on a foil-lined pan in a 350-degree F oven for 10-15 minutes. Otherwise, using the microwave will warm the fish but produce a soggy exterior.