Heat a frying pan or skillet over a high heat. Add the cumin seeds and chilli flakes and toast until they become fragrant. Remove from the heat and pour into a pestle and mortar or spice grinder. Grind into a powder.
Mix half the spice mix with the lamb mince and mix together. Form into four burgers. Sprinkle both sides with a good helping of salt. Heat a skillet over a high heat and sear the burgers until crispy on both sides, about 4-5 minutes on each side. Remove to a foil-covered plate and leave to rest.
In the same skillet add the onion, pepper and chilli along with the rest of the spice mix. Add a drizzle of oil if they look like they're sticking. Cook until caramelised, about 5-10 minutes.
Mix the yoghurt with the garlic cloves. Spread a spoonful of the mixture on the bottom of each of your buns. Top with a burger followed by the pepper mixture and a sprinkling of cucumber chunks and some coriander. Serve with extra yoghurt on the side.