Peel the cucumber and cut in half lengthways. Scrape out the seeds with a teaspoon and cut the cucumber halves into pieces. Crumble the feta and add to the cucumber.
Make the dressing from lemon juice, vinegar, the two oils, salt, pepper, cayenne pepper and sugar. Add the dill and dressing to the cucumber and feta cheese. Mix well and let it steep for a few minutes.
Note: Since the cucumbers give off water and this may water down the salad a bit, you should taste again before serving.