Heat your oven to 180°C/Fan 160°C/Gas 4. Rinse the rice under cold water. Tip it into a small pan and add 300ml hot water from the kettle. Pop on the lid and bring to the boil.
Gently simmer the rice for 25 mins till tender and the water has been absorbed. Take the pan off the heat. Leave it to steam, lid on, for 5 mins to finish cooking the rice.
Pick off the watercress leaves and tender stems and put into a small processor or blender. Pick the mint leaves off the sprigs and add to the watercress.
Trim and roughly chop the spring onion. Peel and grate or crush the garlic. Chop the leaves off the radishes and put to one side fore later. Finely chop the radish leaves then stir them into the spring onions, and garlic into the watercress.
Add 2 tbsp olive oil, 2 tbsp cold water and some salt and pepper. Blitz to make a thick, pesto-like sauce. If you think it's too thick then add more olive oil till you have the consistency you want.
Brush the skin on the salmon fillets with 1 tsp olive oil each. Pop them on a baking tray lined with baking paper. Roast in the oven for 10-15 mins till the salmon is dark pink and opaque.
Roughly crush the radishes with a fork. Warm 1 tsp olive oil in a frying pan. Add the radishes. Stir and fry for 2-3 mins to just heat them through. Warm the watercress sauce in a separate pan. Serve the salmon with the watercress sauce, rice and crushed radishes.