Trim the chicken thighs to remove any excess fat, then pat dry and add the smallest sprinkle of salt, garam masala and turmeric to both sides of the chicken. (This is separate to the measurements you add to your onions later.)
Cook the chicken for 4 minutes on each side on medium heat.
Remove the chicken and set it aside. Add your diced onions to the pan and add the salt, which will draw out the water and help them cook faster. When translucent, after about 8 minutes, add the rest of the spices and cook for 1 more minute to toast the spices and give them more flavor. Add the stock, bring to a boil and then add the chicken back in. Cover and simmer on medium-low heat for 40 minutes.
Turn the heat off, remove the chicken and place it on a plate temporarily. Into the onions and broth, add the lemon juice and the couscous. Give it a stir and then put the lid on and let sit, off heat, for 5 minutes.
Fluff the couscous, add the chicken back in and then add whatever garnishes you like (lemon slices and parsley works well) and serve.