In 2-qt casserole combine mushrooms, carrot, green pepper, celery, onion, garlic and butter; cover.
Microwave at High 4 to 5 1/2 minutes, or until vegetables are tender-crisp, stirring after half the cooking time.
Stir in rice, salt and pepper.
Spoon into two freezer containers.
Label and freeze no longer than 1 month.
To defrost, remove from one container and place in 1- to 1 1/2-qt casserole; cover.
Microwave at High 2 minutes.
Microwave at High 1 to 2 minutes, or until defrosted.
To serve, continue to microwave, covered, at High 2 to 4 minutes, or until heated, stirring once.