Preheat oven (electric cooker: 220 °C/circulating air: 200 °C/gas: see manufacturer). Line baking tray with baking paper. Spread the sandwiches on the baking tray and roast in the hot oven for 8-10 minutes.
Mix mayonnaise, 1 pinch of saffron and 2 Msp. chili flakes. Clean and wash the spring onions, cut them lengthwise into halves and cut them into long pieces.
Spread slices of bread with chilli-saffron mayonnaise. Place spring onions on top. Roughly pluck the fish fillet, spread on top and bake.