Warm mackerel & beetroot salad

More beetroot this week. Straight from Hackney Veggie Box Scheme.
Ingredients:
500g new potatoes, cut into bite-size pieces
3 smoked mackerel fillets, skinned
250g cooked beetroot
100g mixed salad leaves
100g chevre
50g walnut pieces
FOR THE DRESSING Whisk together 3 tbsp olive oil, 1 tbsp wine vinegar or lemon juice and 1 tsp Dijon or other mild mustard. Season to taste, then mix with the horseradish.

Boil the potatoes for 12-15 min until just tender. Meanwhile, 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 salad bowl and season. Tip in the potatoes - they should still be warm.
Add the salad leaves, mackerel, beetroot, chevre and walnuts, and toss gently. Serve with crusty bread, quinoa or brown basmati rice.