In a small bowl mix together the natural yogurt and horseradish, taste and season with salt and pepper.
Slice the beetroot reserving the juice. Arrange on serving plates.
Arrange the rocket salad on serving plates.
Heat a non stick sauté pan over a medium heat. With a sharp knife slice 2-3 cuts into the mackerel skinand place the Mackerel skin side down in the pan and cook gently for 5 minutes or until skin is crispy. Place on top of the salad.
Spoon the horseradish mixture around the plates. Mix the olive oil with 2 tablespoon of the reserved beetroot juice and drizzle over the plates.