Pour the oil in a medium-sized pot and set over medium heat. Add the onion, bell pepper and garlic and cook 3 minutes. Add the rice, cumin, chili powder and cayenne and cook 2 to 3 minutes more. Pour in the stock, increase the heat to high, and bring to a rapid boil. Cover the rice, reduce the heat to its lowest setting, and cook, undisturbed, for 35 minutes, or until the rice is tender.