Heat oil in a large saucepan over medium heat. Sauté chopped onion and sliced mushrooms for 5 minutes.
Drain rice and add it into the saucepan. Stir to coat in oil.
Bring to a boil, then simmer for 20 minutes. Remove from heat and cover with a lid. Let it rest until all liquid is absorbed. *
* This is the failproof method I use for making rice pilafs. Boil it for just 20 minutes and then cover with a lid and remove from heat. The rice will absorb all liquid and you won't risk burning the pilaf.