Rinse the cucumber thoroughly in cold running water. Discard both ends of the cucumber. Thinly (about 0.5 cm (0.2 inches) thickness) slice the cucumber and put them into a large mixing bowl. Add the salt and lightly mix them together. Leave it for 15 mins.
While waiting, thinly slice the onion. Prepare the seasoning sauce by mixing them all together.
Fifteen mins later, rinse the cucumber in cold running water (any remaining salt in the mixing bowl should be discarded) and drain the water out using a strainer. Pat dry the cucumber thoroughly with kitchen paper. Put them into a clean and dry mixing bowl.
Add the sliced onion and the seasoning sauce. Mix them lightly but thoroughly with your hand (You will want to wear a food prep glove).
Put the seasoned cucumber into a sealed glass container and keep it in the fridge for 30 mins to chill then serve. Enjoy!