Whisk together the olive oil, white wine vinegar and seasoning in a small mixing bowl.
Toss the carrot and apple together in a large mixing bowl. Add the dressing and toss well again. Blanch the watercress for at least 15 seconds in boiling water and allow to cool. Spoon into serving bowls and garnish with the cut salad cress. Finish with a few toasted hazelnuts. Serve immediately.