Fire your oven until it reaches 700ºF, and then allow the temperature to fall to about 500ºF, maintaining a bed of coals for sautéing the rice and vegetables and to bake the rice.
Heat a terracotta baking dish in a moderately hot fired oven, and then add olive oil. In the heated pan, sauté the chopped vegetables for 3-4 minutes, or until soft and lightly brow, then remove from the pan. Alternatively, you can sauté the vegetables in a pan on your cook top.
Add the onion, garlic and more olive oil to the empty terracotta pan, and bake for 2-3 minutes, until translucent. Add the rice and stir to coat, and then sauté the rice for 2-3 minutes. Do not brown the rice.
Bake for 20-30 minutes. Rotate the dish a few times if you have coals or a fire in your oven, and one side is hotter than the other.