Step 1

Place spring onion and chilli in a food processor and whiz until finely chopped. Add two-thirds black beans, paprika and breadcrumbs, and whiz until combined. Add chickpeas and remaining black beans, and pulse very briefly so the texture remains a little coarse.

Step 2

Transfer to a bowl and place flour in a separate bowl. Divide bean mixture into six balls, then lightly dust each in flour, shaking off excess. Flatten into 2cm-thick patties. Sprinkle over sesame and flaxseed, lightly pressing seeds into patties.

Step 3

Heat the oil in a frypan over medium heat. In batches, cook the patties for 4-5 minutes each side or until lightly charred and cooked through. Drain on paper towel. Keep warm. Repeat with remaining patties.

Step 4

For the dressing, combine all the ingredients in a bowl and season to taste.

Step 5

Dollop a little yoghurt dressing onto the base of each roll and top with a patty. Divide gherkin, beetroot, radish slices and rocket among rolls. Crumble over the feta, then finish with another dollop of the yoghurt dressing and the bun tops. Serve immediately.