Mash 50g of the butter with the lemon zest, paprika, parsley, a pinch of chilli flakes and some seasoning.
Heat the remaining butter and a drizzle of olive oil in a frying pan. When the butter starts to foam, add the potato cubes. for 15-20 minutes until evenly brown, tender, and a knife goes into them easily.
Season the potatoes with salt and pepper.
Add a knob of the spiced butter to another frying pan, and cook the kippers for a few minutes on each side until cooked through, basting with the butter as they cook.
Put the avocado halves cut-side down on a chopping board and cut thin slices through the avo, lengthways (from top to bottom), arrange on the serving plates and squeeze over a little lemon juice and a pinch of chilli flakes.
Divide the potatoes between four plates and add a kipper to each, with another slice of the spiced butter.