If you follow the recipe closely, you shouldn't have a problem with soggy panko! As the oven temperature is quite high, the topping easily gets nice and crisp. Also, don't forget to add the tablespoon of olive oil to the panko topping before piling it on the fish. This also helps the panko to crisp up nicely. If by any chance your topping is not as crispy as you would like (ovens can vary!) simply pop it under the grill (broiler) for a minute or so. Not for too long as you don't want to risk overcooking the fish!