Cook the lentils in a large saucepan of boiling water for 15 mins or until tender. Drain well.
Meanwhile, heat 2 tsp of the oil in a medium frying pan over medium heat. Cook the onion, stirring, for 5 mins or until the onion softens. Add the cumin, coriander, paprika and turmeric and cook for 1 min or until aromatic.
Process the lentils, onion mixture, chickpeas, tahini and lemon juice in a food processor until almost smooth. Season with salt and pepper.
Place the breadcrumbs on a plate. Shape tablespoonfuls of lentil mixture into small patties to make 16 patties. Dip 1 patty into the breadcrumbs and toss to coat. Place on a plate. Repeat with the remaining lentil mixture and breadcrumbs. Place in the fridge for 30 mins to chill.
Meanwhile, combine the mint and yoghurt in a small bowl. Heat remaining oil in a frying pan. Cook the patties, in batches, for 2-3 mins each side or until golden brown and heated through.
Split open one end of each pita pocket and fill with lentil patties, cucumber, tomato, radish or onion and extra mint leaves. Serve with mint yoghurt.