Bring 2 pans of salted water to the boil and preheat your grill. Place your mackerel fillets in 1 pan and poach for 4 to 6 minutes, or until just cooked. Poach the eggs in the other pan for 3 minutes for a slightly runny yolk, or to your liking. Toast the soda bread, then drizzle with a little oil. Place on a plate and top with the mackerel, a splash of vinegar and a poached egg. Season well, then finely chop and sprinkle with chopped chives.