1. Put butter, mushrooms, celery and onion into an 8-inch round glass cake dish. Cook uncovered in microwave oven 2 minutes at HIGH; stir after 1 minute.
2. Combine eggs, salt, pepper, bean sprouts and chicken; add to vegetables and mix. Cover with plastic wrap and continue cooking about 4 minutes at HIGH; stir every 30 seconds.
3. Remove from oven; stir and allow to stand covered a few minutes before serving.