Chop the cucumber into 1 inch slices, then quarter those into large chunks. Very thinly slice the shallot into rings. Mix together the distilled white vinegar and honey. Add a pinch of kosher salt and stir in cucumber. Mix till well-combined. Refrigerate at least 15-20 minutes.
Before serving, stir in the tomatoes and drizzle on olive oil - about 1 teaspoon or to taste. Sprinkle on the sumac and za'atar, adding more on top as needed when serving. When serving, drain the vinegar mixture so it's not included on the plate/dish. Garnish with parsley, if desired.
Notes
Use seedless cucumbers, a large English or cocktail-sized. This way they don't need to be peeled or de-seeded.
Parsley is optional, but 1 tablespoons of chopped Italian parsley is great on top.
Za'atar and sumac can be found at most grocery stores in the spice aisle. If you can't find za'atar, you can make your own easily with cumin, sesame seeds, thyme, and sumac.
To make ahead - chop the vegetables but keep them separated from the vinegar until you are ready to serve to keep everything as crisp as possible.