Thaw fish, if frozen. Rinse fish; pat dry with paper towels. Cut each fish fillet in half crosswise. Cover; refrigerate till ready to stuff. Prepare Marsala Sauce. Cover surface with plastic wrap and set aside.

For stuffing: In a large skillet, cook onion and garlic in the 2 tablespoons hot butter till onion is tender. Add mushrooms, red sweet pepper, wine, fennel seed, salt, dillweed, thyme and black pepper. Bring to boiling; reduce heat. Boil gently, uncovered, till most of the liquid has evaporated and vegetables are tender (about 6 minutes). Cool slightly.

In a food processor bowl, place vegetable mixture. Cover and process with several on/off turns till mixture is coarsely chopped. (Don't chop the mixture too finely.)

Transfer the vegetable mixture from the food processor to a large bowl. Add the panko or fine dry bread crumbs and crabmeat. Stir to thoroughly combine. (If the mixture seems a bit dry, add a small amount of water to moisten.)

Line a 15x10x1-inch baking pan with foil. Lightly spray the foil with cooking spray. Arrange 8 of the largest pieces of fish on the prepared pan. Spoon about 1/2 cup of stuffing on each piece of fish. For each stack, place one of the smaller pieces of fish on top of the stuffing, skinned side up. (If not baking right away, cover the fish stacks with plastic wrap and refrigerate up to 6 hours.) Drizzle each stack with some of the melted butter. Bake in a 350 degree F oven for 25 to 30 minutes or till instant-read thermometer inserted into stuffing registers 165 degree F and fish flakes easily with a fork. Meanwhile, reheat Marsala Sauce till heated through.

To serve, using a wide spatula, place fish stack on dinner plate. Drizzle with Marsala Sauce. If desired, serve with long-grain and wild rice pilaf. Makes 8 servings.

In a heavy medium saucepan, bring 1 cup Marsala or dry white wine and 2 finely chopped shallots to boiling; reduce heat. Boil gently, uncovered, for 7 minutes. Using a fine-mesh sieve, strain mixture, reserving wine and discarding shallots. Return wine to saucepan. Bring to boiling; reduce heat. Boil gently, uncovered, till wine is reduced to 1/2 cup. Add 2 cups whipping cream, 1/4 cup chopped green onions, 1/2 teaspoon dried dillweed, crushed, and 1/2 dried thyme, crushed. Bring to boiling; reduce heat. Boil gently till mixture is reduced to 11/2 cups, stirring constantly. (Watch carefully so it doesn't boil over.) Remove from heat. Season to taste with salt and pepper. Sauce can be made ahead, chilled and reheated when ready to serve. Makes 1-1/2 cups.