Combine all dressing ingredients in a jar with a lid and shake until well combined, set aside in the fridge.
Cut the rind off of the orange and cut into segments.
Thinly slice celery on the diagonal.
Cut off the top stems of the fennel (these can be used in a stir fry) and remove any discolored outer leaves. Using a mandolin or very sharp knife, thinly slice the fennel bulb.
In a bowl, add celery, fennel and mixed greens, drizzle with dressing, and toss well. Garnish with walnuts and orange pieces, then enjoy!
