Preheat oven to 350 degrees Fahrenheit.

In a dry skillet, brown rice, stirring frequently to prevent burning.

Transfer the browned rice to a 1 1/2 quart casserole dish.

Add 2 1/2 cups of boiling water to the rice.

Stir gently with a fork to separate the rice grains.

Cover the casserole dish.

Bake in the preheated oven for 30 minutes, or until the rice is tender and the water is absorbed.

While the rice is baking, melt 1/2 cup of butter in a skillet over low heat.

Add 1/4 cup chopped onion to the melted butter and saute until softened.

Add 1/4 cup sliced, drained mushrooms to the skillet and saute for a few minutes.

Remove the skillet from the heat.

Add 10 ounces of thawed frozen peas, 8 ounces of drained and diced canned water chestnuts, and 3 tablespoons of soy sauce to the skillet.

Stir to combine the vegetables and soy sauce.

Once the rice is cooked, add the vegetable mixture to the casserole dish.

Gently blend the vegetable mixture with the rice.

Bake uncovered for an additional 15 minutes to allow the flavors to meld.