Spread 1/3 of the bean mixture onto a large flour tortilla - right to the edges. Scatter over some diced tomato, a few fresh spinach leaves, and some grated mozzarella. Roll the tortilla tightly. If you have time, wrap it tightly in cling film, and leave in the fridge for at least 10 minutes - this will help the roll-ups to hold together. Slice with a sharp knife, and serve, drizzled with extra pesto if desired.