All ingredients ready? Let's begin!
In a large salad serving bowl, whisk together the olive oil, lemon zest, lemon juice, salt, and pepper. Set this to the side while you prepare your vegetables.
Trim the fennel by slicing off the green stalks just above the top of the bulb. Remove the fronds with her hands and reserve. The stalks are tough but can be used to add to bone or vegetable broth.
Slice the bulb in half and cut out the dense tough core at the base of the bulb. Cut each half in half again, lengthwise. Slice the bulb quarters as thinly as possible against the grain. Add the fennel slices to the vinaigrette in the bowl and toss to coat evenly.
Cut the onion in half lengthwise. Place each half flat side down and slice as thinly as possible into half-moons. Add the onion slices to the salad bowl.
Remove the skin of orange, and cut into small cubes/chunks.
Add the arugula leaves and gently toss to coat all ingredients with the dressing.
Roughly chop the reserved fennel fronds. You are looking for about 1/4 cup of fronds.
Using salad tongs, place the salad on individual plates and top each with the feathery fennel leaves. Serve immediately and enjoy.