Marinate cleaned chicken pieces with sliced onion, tomato, kashmiri chilli powder, turmeric powder, fennel powder, chicken masala and salt. Add 1/3 cup water to this and pressure cook for 1 whistle on full flame. Switch off the gas and let the pressure drop naturally.
Separate the chicken pieces from the gravy.
Heat oil in a wide pan and shallow fry the chicken pieces till it's golden brown on both sides. Transfer the chicken to a plate.
To the same frying pan (add more oil if required), add crushed garlic and fry well for 2-3 mins. Add the onions and tomatoes from the pressure cooker (excluding the stock/cooking water) to the pan.
Cook till the onions caramelise. Add the stock/cooking water to the caramelised onions and tomato. Bring it to boil. Add fried chicken pieces. Reduce flame to the lowest. Cover and cook till the gravy is almost reduced and chicken pieces are coated well with the masala.
Fry the chopped cashew till it's golden brown. Garnish the cooked chicken with fried cashews and chopped coriander leaves.
Serve the chicken roast with rice/roti/pathiri/appam