To make the dressing, combine the olive oil, lemon juice, salt and pepper in a screw-top jar. Close the jar and shake well to combine.
Cut off and reserve a few of the freshest looking fennel fronds for garnish. Trim the fennel bulbs by removing any green stalks. If the base of the fennel bulb is a little brown, cut a thin slice off. Use a vegetable peeler to remove any brown parts from the sides of the fennel. Cut the fennel bulb in half, then thinly slice using a mandolin or knife and place into a mixing bowl. Pour over the dressing. Lightly toss.
Use a sharp knife to segment (or slice) the oranges and place into the bowl with fennel. Pour over the dressing. Toss to combine, then transfer to a serving platter or bowl.
Serve the Insalata (salad) of orange and fennel with reserved fennel fronds on top – buon appetito.