Heat the oil in a large frypan over medium heat. Add the onion and garlic; cook and stir until onion is translucent. Stir in the chilli powder and cumin, and cook for about 30 seconds. Add the rice, chicken stock and tomato paste and bring to a boil. Transfer to a 1 litre casserole dish and cover with aluminum foil or a lid.
Bake for 35 to 40 minutes, or until liquid has been absorbed and rice is tender. Let rest for 3 to 5 minutes before serving.