Heat oil in a pan over a high heat and add chopped garlic, ginger and a whole green chilli and stir for one minute. Then add the chopped onions and stir for 4 minutes or until softened.
Add turmeric, salt, garam masala, cumin, curry powder, chilli powder and stir for 2 minutes.
Add the chopped tomatoes to the pan and mix. Leave the mixture to simmer until the mixture has thickened. Stir occasionally to prevent the mixture burning.This took me around 2 to 3 minutes.
Add the diced chicken breast into the mixture and mix it evenly into the sauce.
Cover the pan with a lid and continue to cook over a medium heat for 10 minutes or until the chicken has fully cooked.
Remove the lid and add fresh coriander and mix it into the mixture. Then leave the sauce to simmer uncovered for 2 minutes stirring occasionally.