1. Combine Greek yogurt, olive oil, lemon juice, dill, mint, and parsley in the bowl of a small food processor or blender. Process until herbs are finely minced and dressing is well blended. Season with salt and pepper. Set dressing aside.
2. Combine cucumber, tomatoes, and red onions in a large bowl. Lightly sprinkle vegetables with a pinch of salt. Toss vegetables with the dressing and garnish with lemon zest.