Wash and dry produce.
Halve and peel onion; dice onion until you have 2 TBSP (4 TBSP for 4 servings).
Quarter lime and dice tomato.
Trim and quarter cucumber lengthwise and cut crosswise into ¼-inch pieces.
Roughly chop parsley and pick and roughly chop fronds from dill.
In a large bowl, mix diced onion with a squeeze of lime, a pinch of sugar, and a pinch of salt. Set aside.
To bowl with onion mixture, add tomato, cucumber, sumac, dill, parsley, juice from remaining lime, a large drizzle of olive oil, salt, and pepper. Stir to combine.
