Preheat oven to 400 degrees F. Place Reynolds(R) Oven Bag in a 13x9x2-inch pan. Add flour, salt and pepper to bag. Gently squeeze bag to blend ingredients.
Add onion, mushrooms, rice and 1 tablespoon butter to oven bag. Turn bag several time to mix ingredients. Arrange ingredients in even layer in bag. Fold down bag opening two times to hold it open; set aside.
Microwave water and chicken broth in a medium microwave-safe bowl or measuring cup for about 3 minutes on high power until liquid is very hot. Carefully pour or ladle liquid over ingredients in bag. Carefully unfold bag opening.
Close bag at gathers with nylon tie. Cut six 1/2 inch slits in top near tie.
Bake 25 to 30 minutes or until most of the liquid is absorbed. Let stand 5 minutes. Carefully cut top of bag open. Spoon rice mixture into a large serving bowl. Stir in remaining tablespoon of butter and shredded cheese. Stir in up to cup additional hot water, if needed to make mixture creamy. Add additional salt and pepper and garnish with parsley, if desired.