Heat the oil in a small pan and saute the spring onion for 1 minute. Remove from the heat and stir in the salmon. Transfer to a bowl and leave to cool slightly.
Brush the sandwich toaster with a little sunflower oil, wiping off the excess with kitchen paper. Preheat the sandwich toaster to its highest setting.
Stir the Quark, horseradish and Tabasco into the salmon mixture and season with pepper. Spread the salmon mixture on to one slice of bread and top with the second slice. Place the sandwich in the toaster, close the lid and cook for 4 minutes until browned.