Wash the lentils and allow them to soak for 6 hours. After this time, drain them and grind them coarsely in a food processor. Add the rice and mix. Season with salt and pepper and add the diced garlic clove, parsley, tahini and ground cumin. Shape 8 hamburgers with moist hands. Cook the burgers for 4 minutes on each side.
Meanwhile, prepare a sauce by whisking the yoghurt with the cucumber (after peeling, dicing and draining it), a tablespoon of olive oil, the dried peppermint, and a pinch of salt and pepper.
Serve the burgers on the bun with lettuce leaves, thin slices of tomato and onion and a spoonful of yoghurt and cucumber sauce.