Carefully cut open the belly of <quantity>1</quantity> mackerel. Remove the guts with your hands and clean with a paper towel

Make a cut from the belly opening to the head using a pair of scissors. Remove the gills and clean the cavity with a paper towel

Slice along both sides of the spine, from the inside of the belly, without cutting through. Flatten the fish

Cut out the spine with the scissors, being careful not to cut through any of the skin

Cut out the bones in the head and flatten the fish

Remove the rib bones with fish bone tweezers

Add <quantity>¼<unit>cup</unit></quantity> of soy sauce and <quantity>1<unit>tbsp</unit></quantity> of brown sugar to a large, shallow container

Add <quantity>⅓<unit>cup</unit></quantity> of olive oil and mix to combine

Coat both sides of the mackerel with the marinade and leave in the container

Cover with cling film and place in refrigerator for 1h to marinate

Take <quantity>200<unit>g</unit></quantity> of english peas out of their pods

Tale <quantity>200<unit>g</unit></quantity> of fava beans out of their pods

Bring <quantity>2<unit>cups</unit></quantity> of water to a boil in a medium pot. Add <quantity>1<unit>tsp</unit></quantity> of salt

Trim and peel <quantity>1<unit>stalk</unit></quantity> of rhubarb. Reserve the trim and peels

Add them to a saucepan with <quantity>150<unit>ml</unit></quantity> of white wine

Cook over medium heat until the wine has reduced to <quantity>2<unit>tbsp</unit></quantity>. Turn off the heat

Dice the rhubarb into very small pieces

Prepare an ice bath

Add the peas to the water and boil for 30s. Use a skimmer to transfer them to the ice bath to stop the cooking. Remove once chilled

Add the fava beans to the water and boil for 30s. Use a skimmer to transfer them to the ice bath to stop the cooking

Peel the fava beans

Refrigerate the peas and fava beans

Add <quantity>200<unit>g</unit></quantity> of butter, divided in two batches, to the reduced wine. Whisk until just melted and smooth

Press the sauce through a fine mesh sieve

Add the juice and zest from <quantity>½</quantity> lemon

Season with salt to taste and mix to combine

Carefully place the mackerel, skin-side down, on a heated grill for 1m. Flip and grill for 3m until cooked through

Add <quantity>1<unit>tbsp</unit></quantity> of water to a saucepan. Add the peas and beans

Add the rhubarb and butter sauce. Cook over low heat until it starts to simmer and remove from the heat

Cut the mackerel into fillets and portion each of them in half

Spoon <quantity>3<unit>tbsp</unit></quantity> of the green peas and fava beans onto a serving plate. Add 2 pieces of the grilled mackerel

Scatter <quantity>1<unit>tsp</unit></quantity> of the diced rhubarb. Top with sea beans to taste. The mackerel & peas is ready

Enjoy!