Heat the oil in a medium sized frying pan until the oil just starts to shimmer.
Stir in the garlic ginger paste. Gently fry until the garlic ginger paste stops sputtering. This can get a little messy.
Turn your heat down to medium low and add your spice mix. Cook for about 30 seconds. You want to fry your spices in the oil. Don't skimp on the oil. Bad things happen if the spices stick and burn.
Add the green chilies if you are using them. Cook another 30 seconds or so.
Add the Indian hotel curry gravy. Stir it really well to get the oil to combine with the curry gravy. You want everything mixed together at this point. Bring to a simmer.
Add the chicken thigh pieces in a single layer. Nestle them down into the sauce. Cover and ccok about 5 minutes. Remove the cover, flip the chicken and recover. Cook until the chicken is done. Use an instant read thermometer if you have one. You are shooting for an internal temperature of 160F. It will get to 170F as the curry finishes cooking.
Add the garlic pickle (or whatever pickle you decide to use) and the optional naga pickle if using. Stir well to combine.
Look at the consistency. You have a decision to make. If the chicken threw a lot of liquid the sauce might be right. If not, add a tablespoon or two of chicken stock and mix it in. Look again. If you are happy with it, cover and simmer for 2 minutes. If it's still too thick, add a bit morestock. I've never added more than a 1/4 cup.
Achari chicken curry is great with rice and a chickpea curry if you are feeling really motivated.