Preheat the grill to its highest setting.
Place the mackerel fillets flesh-side up onto a grill tray. Sprinkle with crushed cardamom seeds and the grated horseradish and season lightly with salt and freshly ground black pepper.
Place under the grill for 3-4 minutes, then turn and cook the other side for 30 seconds, or until the fish is just cooked through.
For the salad, place the potatoes into a pan of water, bring to the boil and simmer until tender. Drain and leave until cool enough to handle, then peel off the skins.
Meanwhile, bring a large pan of salted water to the boil. Add the cauliflower and cook for three minutes.
Add the beans and cook the cauliflower and beans for three minutes, or until just tender. Drain and set aside.
Heat a frying pan until hot, add the olive oil, anchovy fillets, capers and garlic and fry for one minute.
Add the potatoes, cauliflower and green beans and mix together well.
To serve, place equal portions of the salad into the centre of each dish. Top each with two mackerel fillets and drizzle over any pan juices from the salad.