Heat your frying pan (don't use non-stick) briefly over medium heat. Add the oil.
When the oil starts to shimmer add the garlic ginger paste and green chilies. Cook, stirring constantly, until the garlic ginger paste stops sputtering. Stand back. Wear old clothes. Restaurant style can get messy.
Turn the heat down to medium low and add the spice mix. This step is critical. Stir it constantly for around 30 seconds. If it starts to darken lift the pan off the heat. You want the spice mix to bubble in the oil. That's called blooming spices. Flavour magic happens here. You know the smell of Indian restaurants? This is where it comes from. What you don't want to do is burn the spices. That's a one way trip to starting over. Seriously. There's no coming back. So be a little careful until you get the hang of this.
Turn the heat up to medium high. Add the diluted tomato paste. Stir to combine and cook until little bubbles start to form. This takes around 30 seconds to one minute. You are now in the safe zone. Really hard to burn spices at this point.High heat is important here. You will be frying the curry base, generating all sorts of wonderful flavour compounds. That's more flavour magic. As you become more comfortable with this technique try pushing it. Add 3 oz of curry base. Stir until bubbles form, around 30 seconds. Think lively boil meets frying in oil. Watch the edges of the pan. The curry can stick here. Sticking is OK. Just scrape it back into the curry. Burning is bad.
Add 6 oz of curry base and stir briefly. Let it cook/fry until the bubbles form again. This takes 1-2 minutes.
Add the rest of the curry base and let cook until the bubbles form - another minute or two.
Taste. Every bottle masala mix is different. If you find it well balanced go with it. If it is a little tart add the 1/2 tsp of jaggery or brown sugar.
Turn the heat down to low and add the pre-cooked chicken. Stir to combine.
Let the curry simmer for about 5 minutes. If it gets too thick add a bit more curry base.
Add the halved cherry tomatoes and cook until the tomatoes are just warmed through.
Serve with basmati rice or your favourite Indian flatbread. I was working on a keema biryani recipe when I took the pictures. That was too much. Don't do that.