Bring water to a boil and add butter and salt.
When butter is melted, add in the rice and bring back to a boil. Lower the heat to very low and cover. Allow to cook for 25-30 minutes, until all the water is absorbed. OR make the rice in a rice cooker, adding the butter and salt in with the water.
Take the cooked rice and spread it in a 9x13 pan, allowing it to cool while you work.
In a bowl, combine the sour cream with 1/4 cup of the onion and the cilantro. Salt to taste.
In a pan, saute the garlic and the rest of the onion in the oil. Stir in the peppers and frozen corn. Saute for about 1 minute.
Add the sour cream mixture, vegetables and cheese to the rice in the pan and stir to combine.
Bake at 350 for 30 minutes, or until heated through.