Preheat the oven to 375°F (190°C). Grease a 13-inch by 9-inch baking dish with nonstick cooking spray.
In the prepared dish, whisk together the coconut milk, tomato paste, chicken broth, garlic, garam masala, curry powder, chili powder, ginger, and salt until smooth.
Stir in the onion, rice, and raw chicken (if you're using cooked rotisserie chicken, wait to add the chicken towards the end of the baking time).
Cover the baking dish tightly with foil. Bake for 45 minutes.
After 45 minutes, remove the foil, and stir the mixture. The rice will likely not be done yet, which is fine!
If you're using rotisserie chicken, stir it into the dish at this time.
Cover the dish again, and return it to the oven until the rice is completely tender, typically about 10 more minutes.
Garnish with cilantro before serving.