Take out the bowl from the refrigerator. Add yogurt, cornstarch, mustard oil, tandoori masala powder, Kashmiri red chili powder, turmeric powder, garam masala powder, and black pepper powder to the bowl and mix well to coat the chicken pieces.
Heat charcoal over a direct flame until it is red hot. Keep a small bowl in the center of the marinated chicken and place the heated charcoal on the bowl.
Preheat the oven to 400 degrees F (200 degrees C). Thread the marinated chicken in the skewers along with onions and green peppers. Line the skewers on a foil-lined baking tray.
Grill for 10-12 minutes. Pull the tray from the oven and baste the skewers generously with butter. Flip and baste with butter on the other side as well.
Return the tray to the oven and grill for another 10-12 minutes. Increase the oven temperature to 420 Degrees F and broil the skewers for 3-4 minutes until they are slightly charred. Remove the tikka from the oven and serve hot.