To store your lemon panko fish, place the cooled fillets in an airtight container and refrigerate for up to two days. For reheating, preheat your oven to 375 degrees Fahrenheit. Place the fish on a wire rack over a baking sheet to keep it crispy, and heat for about 10 to 15 minutes or until it's heated through. Avoid the microwave as it can make the panko coating soggy.