Preheat the oven to 180°C/350°F/Gas 4
Firstly roast the beetroot; place the beetroot and rapeseed oil in a foil parcel and place in a medium sized roasting tray making sure the beetroot is well coated in oil. Roast for 45-50 minutes or until the beetroot feels tender. Leave to cool and then skin and cut into bite size pieces. Cut the boiled potatoes in half, then blanch the broccoli in a pan of boiling salted water for 1 minute, then add the peas and cook for a further minute. Drain and then plunge the vegetables into ice cold water and drain in a colander.
Prepare the mackerel by removing the skin and breaking into smallish pieces. Assemble the salad on a plate using the potato, beetroot, peas, broccoli, rocket, salad leaves and cherry tomatoes. Drizzle with lemon dressing and spoon on some of the horseradish dressing, season with black pepper and garnish with alfalfa sprouts.
Tip: If you did not wish to roast the beetroot you could buy and use pre-cooked beetroot
Tip: This is also good if you serve the smoked mackerel hot with the salad