Place the sliced cucumbers into a colander. Salt them well. Leave them to sit for 20 minutes. Pat them dry with a paper towel. This removes most of the excess salt.
Put the sliced onions in a bowl of ice water for 10 minutes.
In a small bowl, combine the olive oil, vinegar, and oregano. After 10 minutes, move the onions to this marinade for another 20 minutes.
Cook the pasta according to the package instructions (less 1-2 minutes for al dente). Drain and run under cold water to stop the cooking.
In a mixing bowl, combine the Greek yogurt, lemon juice, garlic, dill, salt, and pepper.
Mix in the cucumbers, cooled pasta, onions, and some of the marinade. You can add more if the salad seems dry.
Toss everything together well. Taste and adjust for salt and pepper. Serve garnished with a little extra dill.