4 whole mackerel, gutted and scaled
100g salted butter, softened but not melted
1 red chilli, deseeded and finely diced
1 bag watercress
1 clove garlic, finely chopped
Zest of half a lemon
Finely chop a small handful of the watercress. Mix together the butter, chilli, watercress, garlic, and lemon zest. Spoon the butter mixture onto a sheet of cling film, then roll into a tight cylinder, twisting the ends to help it keep the shape. Place into the fridge for 10-15 minutes or until it has set firm.
Using a sharp knife, slash the skin of the mackerel diagonally on both sides. Drizzle with olive oil and sprinkle with sea salt. Remove the butter from the fridge and take off the cling film before slicing into 8 rounds.
Place the mackerel on a pre-heated barbecue, either directly or in a barbecue fish basket. Cook for 3-5 minutes on each side, making sure that you only turn the fish once. After the fish has been turned, place two rounds of butter on each fish and allow it to melt slightly. You will know when the fish is cooked as the flesh will come away easily from the bone.
Place the remainder of the watercress in a bowl, drizzle with olive oil and sprinkle with sea salt. Serve together with the cooked fish and some lemon wedges.