Preheat skillet(non-stick) and saute onion in oil. Add mushrooms and
saute about 2 minutes, stirring constantly, until mushrooms wilt.
Spread half of fillet slices on mushrooms; sprinkle with salt and
pepper; and remaining fillet; sprinkle these with salt and pepper.
Add celery, soy sauce, and sherry; cook gently, covered, for ten
minutes.