1. Preheat oven to 400°F.
2. Season fillets with salt.
3. Saute celery and onion in margarine until tender.
4. Stir in mushrooms, parsley, and lemon juice.
5. Spread mixture over fillets.
6. Roll up fillets and secure with toothpicks.
7. Place in lightly oiled baking dish and bake 20-25 minutes or until fish flakes easily with fork.