Prepare the vegetables, wash them, dry them with a towel and cut them arbitrarily, divide the onion into slices with rings.
A little tip: the salad will look more aesthetically pleasing if you choose vegetables of the same size. Use salad onions, and white, or red - it's up to you. If you use onions, it must be pre-sliced and soaked for 15 minutes in cold water, changing the water to fresh every five minutes. Drain the water, pat the onion with a paper towel and use as intended. This simple procedure will remove excessive bitterness and make the onion crispy and not so sharp.