Core the tomatoes and cut them into roughly 1-inch pieces. Place them in a large mixing bowl, including any juices collected on the cutting board.

Halve the English cucumber lengthwise and cut it into 1/4-inch slices. If the center is unusually watery, scrape out some of the seeds with a spoon before slicing.

Add the sliced cucumber, red onion, basil, and parsley to the bowl with the tomatoes. Toss gently so the herbs are distributed without crushing the tomatoes.

In a small bowl, whisk together the olive oil, red wine vinegar, garlic, Dijon mustard, oregano, salt, and black pepper. The vinaigrette should look lightly thickened and evenly blended.

Pour the vinaigrette over the vegetables: Fold everything together gently, lifting from the bottom of the bowl so the tomatoes remain intact.

Let the salad stand at room temperature for 20 minutes. Stir it once halfway through. The tomatoes will release some juice, creating a light, flavorful dressing.

Toss the salad again and taste: Add a small pinch of salt or a splash of vinegar only if needed. Serve with some of the tomato vinaigrette spooned over each portion.