Place a frying pan over a medium heat and lightly toast the pine nuts for 2-3 mins or until golden. Remove from pan and set to one side.
Put the borlotti beans into a large bowl and mash well with a potato masher or fork. Add the pine nuts, onion, tomato paste, half the breadcrumbs, the thyme and egg. Season to taste, then gently mix together until the ingredients are thoroughly combined.
With slightly wet hands, shape the mixture into 4 burgers. Coat the outside of each burger with the remaining breadcrumbs. Cover and chill in the fridge for at least 30 mins.
To cook the burgers: heat a thin layer of sunflower oil in a large frying pan and fry for
3-4 mins each side until golden. Drain on kitchen paper, then serve in warmed flatbreads, tortillas or pittas and spoon over the Basil tzatziki.