Fry the fish until it is cooked, about 10 minutes.
In the meantime, put the butter in a saucepan, heat gently and let it cook to obtain hazelnut butter (the butter will gradually change colour and give off a characteristic hazelnut smell). Be careful not to overheat your butter, otherwise, it will burn.
Once the butter is nutty, add the lemon juice and zest, then the capers.
Coat the cooked fish with the sauce and sprinkle it with fresh parsley.