To make the dressing - place all the dressing ingredients into a bowl and whisk well to combine. Set aside and make the salad.
Place slices of prosciutto (if using) on a baking sheet lined with baking paper. Place the walnuts on another sheet also lined with baking paper. Put both trays in the preheated oven. Bake the walnuts for ~6-7 mins. Bake the prosciutto for the full 10 minutes or until golden. Set both aside to cool. (See note 1)
Once the prosciutto and walnuts are cooked, assemble the salad in layers by adding ⅓ of the arugula, ⅓ peach slices, and ⅓ goat's cheese into a large bowl. Crush over ⅓ of the cooled walnuts, crumble over 2 slices of cooked prosciutto and repeat this twice more so you have three layers. (See note 2 for more tips).
Drizzle ⅔ of the dressing over the top and serve straight away. More dressing can be added to each bowl once served if desired.
Video
Notes
1) If the walnuts smell and look cooked in your oven well before the 7 min mark take them out. You don't want them to burn. Same goes for the prosciutto. It's done when crispy and may need more or less than 10 mins depending on how hot your oven runs.2) I layer this salad, so it doesn't need to be tossed and looks beautiful when served. You should have three layers of arugula/rocket, peaches, goat's cheese, and walnuts when done. 3) The dressing is generous so if any is left, keep it in a jar with a lid on in the fridge. It can be used within the week for another salad.