Wash and clean the cucumber and cut into thin strips. Peel and halve onions and cut them into thin slices. Mix the prepared ingredients in a bowl. Add vinegar and 3 tablespoons of oil, season with sugar, salt and pepper and mix everything together.
Simmer eggs in boiling water for about 10 minutes, rinse with cold water and peel. Finely chop the eggs. Wash parsley, shake dry, pluck leaves from stalks and chop finely. Wash the chives and cut into fine rolls. Mix sour cream, yoghurt, chopped eggs and herbs in a bowl, season with salt and pepper.
Wash the fish, dab dry and cut into 12 long strips (approx. 2.5 cm wide). Season with salt and pepper. Put quinoa in a deep plate, turn the fish in it. Heat the rest of the oil in a large coated frying pan, fry the fish for about 5 minutes in portions, turning, remove and drain on kitchen paper.
Cut cress from the bed. Arrange herb dip, fish and cucumber salad on plates. Sprinkle with cress.