Wash, dab and finely chop the onions and tomatoes. Wash the peppers, dab, cut in half lengthways, remove the seeds, then also finely chop.
Put the washed rice in a saucepan, add the vegetable stock and enough water so that there is about 2 cm of liquid above the rice. Add the remaining ingredients, stir and cover the pot with a loosely fitting lid.
Bring everything to a boil, then let it steep on the lowest setting for about 15-20 minutes with the lid loosely closed. Stir well and season to taste. If the rice is not done yet, add a little more hot water and let it steep for another 5 minutes.