Use a mandolin to thinly slice the fennel bulbs, apples, and celery stalks. You can also use a sharp knife if a mandolin isn't available--try to slice as thinly as possible. Place in a large bowl and toss to combine.
In a small bowl, whisk together the lemon juice, honey, dijon, salt, and pepper. Slowly, while whisking, add the olive oil.
Drizzle dressing over the salad. Add the toasted pecans and toss to combine.
Plate salad, and top with freshly grated parmesan and fennel fronds. Enjoy!