Halve the fennel and thinly slice with a mandolin or very sharp knife.
Segment the oranges over a bowl to catch any juices. Whisk together the orange juice, oil, shallots, salt and pepper. Add the fennel, orange segments and spinach, and toss to coat.
Divide the salad among 4 plates and top each with 5 olives. Top each salad with cheese and the reserved fennel fronds.
Yield: 4 servings