Boil or steam the potatoes for 12-15 mins until just tender. While the potatoes are cooking, flake the mackerel fillets into large pieces and cut the beetroot into bite-size chunks.
Drain the potatoes and cool slightly. Mix the salad dressing and horseradish sauce together in a bottle and shake well. Taste and adjust for seasoning.
Tip in the potatoes (preferably still warm) into a salad bowl. Add the salad leaves, mackerel, beetroot and celery, add as much dressing as desired and toss gently to coat. Sprinkle with the pecan nuts and serve immediately with good crusty bread for mopping.
Recipe by Cooksister | Food, Travel, Photography at http://www.cooksister.com/2014/04/smoked-mackerel-beetroot-potato-salad.html