Peel and seed the cucumber. Grate or slice it and sprinkle it with salt. Let it sit for half an hour before tipping it into a colander or strainer and pressing all the water out. Taste a piece of cucumber. If it’s unbearably salty, give the cucumber a quick rinse and press out all the water again. Stir the cucumber into the yogurt. Now is the time to add onion and chiles, if