If desired, chop the onion using a mandolin slicer and toss it in a hot pan with a couple of table spoons of oil and a dash of salt. Leave it to sweat on a small to medium heat for 2 to 3 minutes until the onion starts turning translucent and then toss in the chopped garlic for another minute or so.
While the onion is cooking, take the cumin seeds, the coriander seeds and the cinnamon and crash them together in a fine powder using a mortar.
In a big bowl, add the powder just created, the onion and garlic, the salt, the turmeric, paprika, chopped cilantro and mint, squeeze the juice from the lemon and perhaps add a cup of chicken stock, water, or, if you are feeling adventurous, yogurt and mix everything thoroughly.
Once you have your marinade, you can add the chicken breast either whole or cut into strips using a well sharpened knife and leave to marinate anywhere between 2 and 4 hours.
Let as much of the marinate drip off the chicken, lightly pat it down, and throw it on a hot grill, ideally charcoal, but a grill pan is almost as good.
Allow to cook between 7 and 3 minutes per side on the grill, but the best indicator that the chicken is done is if you have some nice grill marks on both side of the chicken.