Tip the rice into a small pan. Pour in 400ml boiling water. Add a pinch of salt. Cover. Bring to the boil, then turn the heat down and very gently cook for 15-20 mins till the water has been absorbed and the rice is sticky. Take off the heat.
Meanwhile, make the dressing. Zest the lime into a bowl and squeeze in the juice. Peel and grate in the garlic and ginger. Add 2 tbsp of the tamari, 1 tbsp olive oil and ½-1 tbsp of the horseradish mustard (horseradish mustard is hot so use as much or little as preferred). Stir well to combine.
Trim and peel the carrots. Use the peeler to create thin carrot ribbons, peeling down to the core and then thinly slicing the core. Trim the courgette and peel it into matching ribbons, slicing the seeded core. Peel and thinly slice the red onion. Tip the carrots, courgette and onion into a bowl. Toss in the watercress. Pour over the dressing and toss everything together till evenly coated.
Allow the rice to cool slightly then spoon into bowls. Top with the dressed vegetables and spoon over any remaining dressing.