1. Trim the stalks and root ends from the fennel bulbs. Pull off any tough and bruised outer layers. Cut the bulbs in half and cut out most of the core, leaving just enough to hold the layers together. Slice bulbs on an angle through core into thin slices. 2. Whisk olive oil, lemon juice, salt and pepper in small bowl until blended. Add sliced fennel and red onion and toss until coated. Let stand at room temperature, tossing occasionally, about 1 hour before serving.
Cook's Note: This salad can be made up to 1 day in advance, omitting the onion. Bring to room temperature, add the onion, toss once or twice and check seasonings before serving.