Cook the rice as you ordinarily would but stir in the masala paste before switching on the rice cooker. Sprinkling with salt is optional. When done, fluff up the rice by raking through lightly with a fork.
Heat the butter in a frying pan or wok. Add the vegetables, onion and garlic. Sprinkle with salt. Stir fry for about a minute to a minute and a half depending on your choice of vegetables and the size of the cut.
Add the mushrooms, sprinkle with salt once more and cook for 30 to 45 seconds depending on the size of the mushrooms.
Add the rice. Stir and toss just until heated through.
Sprinkle with scallions.
Serve the masala rice with oyster mushrooms and vegetables at once.