Cut off and discard fennel stalks.Trim base and remove any wilted outer layers. Cut into quarters lengthwise and remove core. Using a mandolin or very sharp knife, thinly slice fennel. In a mixing bowl combine fennel and lemon juice; toss to combine. Just before serving drizzle with olive oil and season to taste with salt and freshly ground black pepper. Add parsley; toss to combine.Top with Parmesan, if desired.