Cut the fillet into large enough, but uniform pieces and put in a container for marinating.
Prepare the marinade in a separate bowl. To do this, squeeze the juice from the lemon and mix with the onion grated. In the resulting slurry add mustard, which is better to take not too strong, butter and dry ground herbs and spices.
Stir the marinade and add a little salt to taste.
Pour the fish with marinade, mix well and leave for an hour and a half for soaking.
After time, string fish on skewers or skewers. If wooden skewers are used, then they must be soaked for 10 minutes in cold water before stringing.
Cook on the grill or in the oven for about half an hour.
During cooking in the oven, you must not forget to turn the barbecues so that they are browned on all sides.