Wash the cucumber. If using an English or Persian cucumber with thin skin, you can leave the skin on. Cut off the ends, then slice the cucumber in half lengthwise and scoop out any watery seeds with a spoon if they are large and watery. Slice the cucumber into 1/4-inch half-moons (or quarter-rounds if cucumber is large). Transfer to a large mixing bowl.

Prepare tomatoes

Wash the tomatoes. Core and cut into roughly 1/2- to 3/4-inch pieces — wedges for round tomatoes or 1/2-inch slices and then quartered for Roma. Add to the bowl with cucumber.

Prepare onion

Peel the red onion and slice very thinly. Separate the rings and, if you prefer milder onion flavor, soak the slices in cold water for 5 minutes then drain and pat dry. Add the drained onion to the bowl.

Add herbs and cheese

Roughly chop the parsley and add to the bowl. If using feta, crumble it and add to the vegetables but reserve a small amount for garnish.

Dressing

In a small bowl or jar, combine the extra-virgin olive oil, fresh lemon juice, red wine vinegar, Dijon mustard, honey (if using), minced garlic, kosher salt, and freshly ground black pepper.

Whisk vigorously (or tighten jar lid and shake) until the dressing emulsifies and becomes slightly thickened and glossy. Taste and adjust seasoning: add a pinch more salt or a drop more lemon juice if needed.

To finish

Pour the dressing over the vegetables and gently toss with a large spoon or salad tongs until everything is evenly coated. Let the salad rest for 5–10 minutes at room temperature to allow flavors to meld. Taste once more and adjust salt or pepper if needed.

Transfer to a serving bowl, garnish with the reserved crumbled feta (if using) and a few extra chopped parsley leaves, and serve. The salad is best served within 1–2 hours of dressing; if making ahead, store dressing separately and toss just before serving.