Heat the oil in a nonstick wok or frying pan and stir-fry the onions for about 3 minutes. Using a slotted spoon, remove the onions from the wok and set aside to drain.
Mix together the lamb, cumin, ground coriander, tomato paste, chili powder, salt and lemon juice in a bowl and set aside.
Reheat the oil and stir-fry the onion seeds and curry leaves for 2-3 minutes.
Add the lamb and spice mixture and stir-fry for about 5 minutes, then pour in the water, lower the heat and cook gently for about 10 minutes, until the lamb is cooked through.
Add the peppers and half the cilantro and mint. Stir-fry for another 2 minutes.
Finally, add the onions and the remaining chipped cilantro and mint.