Drain the kidney beans and place in a bowl and mash with a fork until soft but still retaining some bean shapes. Add the coriander, half the chilli, the ground spices, spring onions, egg yolk and breadcrumbs and mix well. Form into 4 patties.
Heat 3–4 tablespoons vegetable oil in a large, heavy-based frying pan and cook the burgers over a medium-high heat for 2–3 minutes on each side until browned. Keep warm while making the salsa.
For the salsa, place the tomatoes, olive oil and coriander in a bowl, add the remaining chilli and the spring onions and stir well to mix. Season with a little pepper.
Serve each burger in a soft wholemeal roll with a few rocket leaves and some of the tomato salsa.