Heat the oil in a saucepan and fry the diced onions.
Add the garlic and all of the spices.
Add the chopped tomatoes and water and simmer.
Remove from the heat and add the chicken tikka pieces.
Cook the rice in chicken stock following the package instructions.
Fry the sliced onions until golden brown.
In a large pot, assemble your biryani as follows: 1/3 basmati rice, 1/2 chicken curry mix, 1/2 golden sliced onions, 1/3 rice, oil, 1/2 chicken curry mix, 1/3 basmati rice and finally the re-maining caramelised onions.
Place the lid on and bake in the oven for 10 minutes.
Remove from the oven, add the chopped coriander and sliced green chilli.