Preheat oven to 200°C/gas mark 6. Place the hazelnuts in a small tray and roast for 10-12 minutes, tossing them halfway through, until they are golden. Remove from the tray and leave to cool.
Cut each beetroot into 8 pieces, then place in a food processor and pulse until roughly the size of grains of rice. Place a frying pan over a medium heat with the olive oil, and cook the beetroot for 3-4 minutes, stirring regularly, until slightly softened. Transfer to a plate to cool down.
Meanwhile, combine the dressing ingredients and season.
Once the beetroot has cooled down, combine it with the watercress in a large bowl, add the dressing and season to taste. Divide between 2 plates and top with the crumbled goat's cheese and hazelnuts.