Heat the oil in a medium sized frying pan until the oil just starts to shimmer.
Add the onions and green peppers and stir every few seconds. Keep the peppers skin side down as much as you can. Fry until the pepper starts to blister and the onion edges turn brown.
Stir in the garlic ginger paste. Cook until the garlic ginger paste stops sputtering.
Turn your heat down to medium low and add your spice mix. This is why you need to use all the oil. You want to fry your spices. Too little oil and you risk your spices sticking or burning. Nothing you can do will fix burned spices.
It might look a little dry after frying the onions and peppers. You want the spices in oil. Not a dry paste. If it does look dry add a spash of oil immediately. Cook your spices for about 30 seconds.
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.
Cover loosely and cook for about 5 minutes.
Add the chicken tikka and the green chilies. Continue to cook for about 2 minutes to warm the chicken through. Add the tomatoes and cook another minute or so. At this point your sauce is going to be a little thick. Stir in a tablespoon or two of chicken stock or water to get the consistency you want. As much liquid as you need. This step is feel.
Taste. You have a decision to make. A 1/4 tsp of naga pickle mixed in at this point is a nice touch. It kicks the heat up though but it does add a distinctive flavour you can't get any other way. I like it both ways. Depends on my mood. The more classic jalfrezi leaves it out. Up to you.
Serve with rice, dal and Indian flatbreads of your choice.