1) For the pistachio pesto: combine the parsley, pistachios, thyme, and garlic cloves in the bowl of a food processor; blend until finely chopped. With the machine running, gradually add the olive oil, processing until well blended. Season the pesto with salt and pepper, to taste.
2) For the fennel slaw: place the fennel in a large serving bowl. Add the pesto and toss to coat well. Tear the prosciutto into 2.5cm pieces and add to the bowl. Gently toss to combine. Serve.