Preheat oven to 425°F. Toss potatoes and onions with 1/2 cup of the Seafood Sauce. Spread evenly in greased 13x9-inch baking dish; cover with foil.
Bake 30 minutes or until potatoes are almost tender. Meanwhile, brush remaining 1/4 cup Seafood Sauce over fish and tomatoes. Refrigerate 30 minutes.
Arrange fish and tomatoes over potatoes. Bake 8 to 10 minutes or until fish flakes easily with a fork and potatoes are tender. Garnish with olives, if desired.