Wash and dry cucumbers and tomatoes. Slice cucumbers thinly and halve the tomatoes. Thinly slice the red onion and place all vegetables in a large mixing bowl.
Whisk together olive oil, lemon juice, Dijon mustard, minced garlic, honey, salt, and pepper in a small bowl or jar. Taste and adjust acidity or salt if needed.
Pour dressing over the vegetables, add chopped herbs and optional cheese, and gently toss to combine. Let sit 5–10 minutes for flavors to meld, then serve.
Notes
Soak red onion slices in cold water for 10 minutes to reduce sharpness if desired.
If cucumbers are watery, sprinkle with a little salt and let drain in a colander for 10 minutes before patting dry.
Store in an airtight container in the fridge for 2–3 days; drain any accumulated liquid before serving.