Fill a large mixing bowl with cold water. Add the tablespoon of lemon juice and the apple slices. This will keep the apples from browning.
Spread the baby spinach and micro greens out on a large platter, scatter the sliced celery, fennel, fennel fronds, and walnuts over the top of the greens.
Remove the apples from the lemon water and dry in a salad spinner or with paper towels. Tuck the apple slices in between the spinach leaves and across the top of the salad.
For the dressing
In a mason jar combine the olive oil, apple cider vinegar, tarragon, lemon juice, and sugar. Seal the lid tightly and shake vigorously until the mixture is emulsified. Serve immediately.
