As more headroom is needed when boiling rice or pasta in the microwave, use a larger container than when cooking conventionally.

Place rice and mushrooms in 3 quart casserole. Stir in onion soup, hot water and bouillon. Microwave for 5 minutes on High power (100%) until boiling. Stir, reduce heat to Medium power (50%), and continue to cook for 15 minutes. Fluff with fork, and let stand another few minutes before serving.