Boil the egg in boiling water for about 8 minutes, cool, peel and cut into slices. Cut the cucumber (with the skin) into slices. Halve the tomato, remove the stem and cut into slices. Cut the spring onion into fine rolls.
Brush the bread slice with mustard (instead of butter) - spread the herb quark on top. Place the egg slices on the quark and season. Arrange the cucumber and tomato slices nicely over the bread and on the edge of the plate and season. Sprinkle everything with the spring onion rolls.