Heat the oil in a nonstick frying pan. Add the salmon, skin-side down, and cook for 4-5 mins. Turn and cook for a further 3 mins, or until just cooked through. Transfer to a plate or board and remove and discard the skin. Flake the fish into large chunks.
Meanwhile, combine the dressing ingredients in a jug. Set aside.
In a large bowl, toss the avocado, radish, spring onion and watercress.
Divide the salad mixture and flaked salmon between 4 bowls. Drizzle over the dressing and top with a sprinkling of toasted sesame seeds.