Trim the fennel bulb by cutting off the stalks and removing any tough outer layers. Slice the bulb in half lengthwise, then use a sharp knife to slice it as thinly as possible.
Prepare the oranges by cutting off the top and bottom. Stand the orange on one flat end and cut downward along the curve to remove all peel and white pith. Carefully slice between the membranes to release the orange segments.
Combine the sliced fennel and orange segments in a large bowl.
In a small jar, whisk together the olive oil, lemon juice, salt, pepper, and any optional dressing ingredients until well emulsified.
Drizzle the dressing over the fennel and orange mixture.
Toss gently to coat all ingredients evenly with the dressing.
If using any optional ingredients like fennel fronds, mint leaves, olives, pine nuts, or red onion, fold them in now.
Let the salad rest for 5-15 minutes before serving to allow flavors to meld.
