Rinse and julienne the celery into thin matchsticks.

Using a mandolin slicer, thinly slice the apple, then cut the slices into matchsticks as well (you can do all of this with a knife if you don't have a mandolin slicer).

Toss together the celery and apple in a large bowl.

In a small bowl, whisk together the lemon, olive oil and mint. Season with salt and pepper.

Drizzle the dressing over the celery and apple, tossing a bit to coat. Serve immediately.