Julian Metcalfe, founder of U.K.-based fast-casual superstar Pret a Manger, has a new cookbook out featuring recipes from his new fast-Asian concept, Itsu. Think high-protein, low-carb salads, brown rice, sushi, soups and noodles — fresh food that tastes as good as it looks. Here’s hoping it opens Stateside, and in the meantime, try out one of its most…