In a small Dutch oven, combine the rice and margarine and then cook over medium heat for 2 minutes until the rice is transparent. Add the green onions and then continue to cook for 1 minute until tender. Stir in the water.
Cover the pot and then bring to a boil. Reduce the heat to low, and then continue to cook for 20 minutes, or until all of the water has absorbed.
Add the vegetables and then cook for 5 minutes, until the vegetables are tender.
Fold in the tuna and the soy sauce and then serve hot.