Boil the barley for about 15-20 mins in a pot of lightly salted water until tender, but still al dente.
Transfer into a colander and cool under fresh running water, then drain well.
In the meantime, prepare the pea pesto. In a food processor add cooked peas, lemon zest, garlic, pine nuts, olive oil and a generous pinch of sea salt and black pepper. Blend until smooth for about 1 minute, scraping down the edges with a spatula half-way through.
In a large salad bowl mix together cooked pearl barley with ⅔ of the pesto (store the remaining pesto for another day).
Add in rocket leaves and Grana Padano shavings and give it a nice mix.
With the help of your hands roll each slice of Prosciutto di San Daniele into the shape of a rose, and place on top of the salad.
Add some optional freshly cracked black pepper and serve immediately.
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Notes
The pea pesto ingredients are enough to make a big pot of pea pesto.You can add as much as you like to the salad and store the remaining pesto in the fridge for up to 4 days, or in the freezer for up to 1 month.For a more lemony note, you can swap lemon zest with the juice of half lemon.