Heat a frying pan over a high heat until hot, then add the 2 tablespoons olive oil. Season the salmon and place it, skin-side down, in the pan. Cook for 4 minutes, then turn the fish over and cook for a further 2 minutes.
Meanwhile, heat a separate small dry frying pan until hot, add the orange halves, cut-side down, and sear until starting to char. Remove the oranges from the pan and squeeze the juice back into the pan. Bring the juice to the boil and reduce it to about 1 tablespoon. Whisk in the extra virgin olive oil, then season.
Make the salad. Stone and peel the avocados, then cut into 1 cm (½ inch) dice and place in a mixing bowl. Add the remaining ingredients and season.
Spoon the salad into the centre of each plate. Place a piece of salmon on top and drizzle with the burnt orange vinaigrette.