In a small bowl, combine the indian restaurant mix powder, turmeric, Kashmiri chili powder, cumin, kasoor methi and salt. This is your spice mix. It goes in after the garlic ginger paste.
Heat 4 tbsp vegetable oil in a pot over medium heat until it shimmers.
Toss in the cinnamon bark and green cardamom. Let cook about 20 seconds. You will see little bubbles forming around the bark.
Add the garlic ginger paste and green chilies. Cook until the garlic ginger paste stops spluttering.
Turn the heat to medium low. Add the spice mix. That's the mix you made above and put in the small bowl - not just the Indian restaurant spice mix. Stir continuously until it starts to smell really good. This takes around 30-40 seconds. Watch it carefully. If you burn the spices at this point you have to start over. This is called blooming the spices. It is one of the secrets to Indian cooking.
Add the diluted tomato paste and stir to combine. Turn the heat up to medium. Cook for 1 minute.
Add half the onion paste and turn the heat up to medium high. Stir to combine. Cook for about a minute. Add the rest of the onion paste and stir again. Cook, stirring occasionally for about 4 minutes. Don't worry if it looks dry. The chicken will release juices as it cooks. Instant delicious.
Turn the heat down to medium low. Add the chicken and stir. Cover and simmer until the chicken is done. It's done when you measure the internal temperature and it says 170F, about 12-15 minutes. An instant read thermometer is a handy thing to have here...
If the curry is a bit thick add a bit of water or chicken stock and stir. Add the diced tomatoes and cilantro. Let the chicken masala simmer another minute or so. Taste for salt and adjust as needed.
Garnish with a bit more cilantro if desired.