Prepare the vinaigrette by whisking together the grated sweet onion, apple cider vinegar, honey, salt, and pepper in a small bowl.

Slowly drizzle in the olive oil while whisking vigorously to create a stable emulsion. Set aside.

Trim the fennel bulb and use a mandoline to shave it into thin translucent slices.

Supreme the oranges by cutting off the top and bottom, removing the peel and pith, and slicing between the membranes to release the segments.

In a large mixing bowl, toss the arugula and shaved fennel with half of the sweet onion vinaigrette.

Transfer the dressed greens to a chilled serving platter.

Arrange the citrus segments and sliced avocado decoratively over the greens.

Drizzle the remaining vinaigrette over the avocado and citrus.

Garnish with chopped fennel fronds and serve immediately.