Boil penne pasta according to package instructions, drain, and rinse with cold water to cool
Dice cucumber and halve cherry tomatoes
Submerge sliced red onion in a bowl of cold water for 5 minutes to reduce sharpness, then drain
In a large bowl, combine cooked pasta, cucumber, cherry tomatoes, olives, and crumbled feta
Whisk olive oil, lemon juice, oregano, salt, and pepper in a separate bowl
Pour dressing over salad and toss gently to combine
Refrigerate for 15-30 minutes before serving to let flavors meld