1 medium fennel bulb, cored and thinly sliced lengthwise
Using a small, sharp knife, peel the oranges, removing the bitter white pith. Slice the oranges 1/4 inch thick.
In a very large bowl, combine the olive oil and vinegar and season with salt and pepper. Add the sliced oranges, chopped romaine, shredded radicchio and sliced onion and fennel and toss well. Serve the salad right away.