Purée half of the chopped mango and mix with the remaining mango, tomato, chilli flakes, and mint to make the salsa.
Preheat the oven to 220°C.
Toss the spring onions in olive oil on a baking tray and bake for 10 minutes.
Combine the grated sweet potato, yoghurt, and egg yolk to prepare the rösti mixture.
Heat olive oil in a pan and cook the potato mixture inside a ring mould for 5 minutes.
Remove the mould and fry the other side of the rösti until golden.
In a separate pan, fry the salmon skin-side down for 3 minutes per side.
Assemble the dish by layering the salsa on the rösti, followed by the spring onions and salmon.