Stuffed Fish Fillets au Gratin

• 8 sole, tilapia or whitefish fillets (about 2 lb/1 kg)
• salt

Sprinkle fish lightly on both sides with salt, pepper, paprika and thyme. Arrange half of fillets in single layer in sprayed 7- x 11-inch glass baking dish.

Steel Blade: Process onion and celery with quick on/off pulses, until coarsely chopped. Melt 1 Tbsp butter or margarine in large nonstick skillet; add onion and celery. Repeat with bell pepper and mushrooms. Add to skillet an