Slice the tops off the fennel bulbs and cut them in half lengthwise. Remove the coarse outer shell of the fennel bulb, rinse, lay flat and cut into thin, lengthwise slices.
Cut the top and bottom off of the oranges and lemons, then slice the peel off the citrus, keeping them round in shape.
Remove any excess pith off fruit, cut quarter-inch slices horizontally and pick out seeds with a paring knife.
On a large flat serving platter, layer the fennel and arrange the citrus slices on top. Sprinkle with the olives, parsley and fennel fronds. Season with salt, freshly ground black pepper and a pinch of red pepper flakes, if using.
Drizzle with olive oil and allow salad to marinate before serving, 5 minutes.