Clean the vegetables by thoroughly washing them under cold water, using a vegetable brush if needed.

Slice the cucumber into thin half-moons, julienne or shred the carrots, and slice the celery thinly.

In a medium-sized bowl, combine lemon juice, olive oil, Dijon mustard, and optional maple syrup or honey, whisking to create a smooth dressing.

In a large mixing bowl, combine cucumber, carrot, celery, and red onion, gently tossing to distribute.

Drizzle the dressing over the vegetables, mixing gently to coat without crushing the veggies.

Garnish with chopped fresh parsley and let the salad rest for 5 to 10 minutes before serving.