For the salsa, purée half the chopped mango and add to the remaining mango flesh. Add the tomato, chilli flakes and mint.
Heat the oven to 220C/425F/Gas 7. Place the spring onions in a baking tray dressed in the oil. Bake for ten minutes.
To make the rösti, mix the potato, yoghurt and egg yolk.
Heat the oil in a frying pan and flatten the potato mix into a ring mould in the pan. Fry for 4-5 minutes. Remove ring and fry on other side until golden.
Meanwhile, in another pan heat a drizzle of olive oil. Pan-fry the salmon placed skin-side down for 2-3 minutes each side.
Serve the salsa on top of the rösti, topped with the spring onions and salmon steak.