Grate the cucumber on a fine grater and salt it. Let it stand for 20 minutes and then "squeeze it out" properly.
Add sour cream to the cucumber, add finely chopped onion, olive oil and lemon juice. Mix everything thoroughly and put it in the fridge for at least half an hour so that the flavors combine.
Serve it as a salad with the main meal or as a dressing, for example with grilled meat.