1. Normally, chicken tikka uses boneless chicken. Use if available.
2. For tomato paste, I pureed two tomatoes, that weighed approximately 215 gm without adding any water, and also used a 135 gm packed of tomato paste to give a rich color.
3. The recipe I used had a proportion of 75:25 of chicken and mushrooms. You can try that proportion if interested. Add the mushrooms when the chicken is 3/4 done.
4. Add water if the masala is sticking to the pan. I didn't add any, as the stock from the chicken was more than enough. In case you need more curry, then add some water, but not too much.
5. I only used coriander for garnishing. You can drizzle some cream and sprinkle some ginger julienne as well.