Slice the Persian cucumbers into thin rounds, about 1/8-inch thick. For best results, use a mandoline slicer if available.
Thinly slice the red onion into half-moons. For a milder flavor, soak in ice water for 5-10 minutes, then drain and pat dry.
Place the sliced cucumbers and red onion in a large mixing bowl.
Add the chopped fresh dill and mint (if using) to the bowl.
Add cherry tomatoes and pomegranate seeds if using.
In a small bowl, whisk together the lemon juice, olive oil, minced garlic (if using), sumac (if using), salt, and pepper.
Pour the dressing over the vegetables.
Toss gently until everything is evenly coated with the dressing.
Taste and adjust seasonings if needed.
Serve immediately for maximum crispness or chill for 15 minutes before serving to allow the flavors to meld.
