Combine oatmeals, flour, and salt, then stir in melted butter and hot water to form a smooth dough.
Roll dough into balls, flatten into cakes, and fry for 8-10 minutes per side until golden.
Soften white leek parts in half the butter, add potatoes, and 150ml boiling water.
Cook potatoes covered for 20 minutes, scraping the pan and adding water to prevent burning.
Grill mackerel fillets for 5 minutes, then flake into chunks and discard skin.
Make a roux with remaining butter and flour, then whisk in milk and green leeks to create a thick sauce.
Stir two-thirds of the cheese into the sauce and season.
Layer potatoes and mackerel in a dish, cover with sauce and remaining cheese, and grill until bubbling.
Fry walnuts in butter for 4 minutes and combine with salad ingredients.
Blend oil, vinegar, cordial, and chilli powder to create the dressing.
Toss salad with dressing and serve with warm oatcakes and the hot stovies.