Season the chicken pieces with salt and marinate in a bowl with the garlic, chilies, half the sliced onions and lemon juice. After a few hours in the fridge, add the oil and transfer the mix to a large saucepan or stew pot.
Add a small cup of water and cook over a medium heat, covered, for 30 minutes, until the chicken is cooked through, adding a little more water if it is drying out. Strain and reserve the excess liquid, and finish the chicken by grilling it for 15 minutes or so on a barbecue or in the oven.
In the meantime, return the liquid to the stove and reduce, adding a little oil and the rest of the finely sliced onions. Cook over a medium heat for twenty minutes, adding more lemon juice and chilies if you like. When the chicken is well-browned, place it onto a serving plate and pour the sauce over it.