Cut the salmon fillet into 4 pieces, season with salt and pepper and drizzle with lemon juice.
Heat the oil in a pan and fry the fillets there for about 6 minutes.
In the meantime, peel the cucumber, cut in half lengthways, core and cut into slices.
Halve the onions and cut into thin slices, then fry them in the oil. Add the cucumbers, pour the cream on top and sauté for about 10 minutes. Finely chop the herbs and mix with the vegetables with the horseradish. Season everything with salt, pepper and lemon juice.
Serve the cucumber vegetables with salmon and sprinkle with chives if desired.