In a large saucepan, bring water, rice and peas to a boil. Reduce heat; cover and simmer for 20-25 minutes or until tender. Drain and set aside.
In a skillet, saute the mushrooms, celery, carrots, onion and garlic in oil until vegetables are tender. Combine the vegetables, rice mixture, tomatoes and seasonings.
Transfer to a greased 2-1/2-qt. baking dish. Cover and bake at 350 degrees F for 30 minutes. Uncover; sprinkle with cheese. Bake 5-10 minutes longer or until the cheese is melted.