Preheat oven to 400°.
Heat 1 teaspoon oil in a small skillet over medium-high heat. Add shallots; sauté 3 minutes or until tender and lightly browned. Add garlic; sauté 30 seconds. Spoon shallot mixture into a food processor. Add 1/2 cup tomatoes, parsley, juice, 1/4 teaspoon salt, 1/4 teaspoon pepper, and Old Bay seasoning; process just until combined. Spoon shallot mixture into a bowl; stir in panko.
Place each fillet between 2 sheets of heavy-duty plastic wrap; pound to 1/2-inch thickness using a meat mallet or small heavy skillet. Spoon about 1 1/2 tablespoons shallot mixture on the small end of each fillet. Beginning with small end, roll up jelly-roll fashion; secure with toothpicks. Arrange rolls on a jelly-roll pan coated with cooking spray. Drizzle with 2 teaspoons oil; sprinkle with 1/8 teaspoon salt and 1/8 teaspoon pepper. Add remaining 1/2 cup tomatoes and wine to pan. Bake at 400° for 25 minutes or until fish flakes easily when tested with a fork or until desired degree of doneness.
Heat remaining 1 1/2 teaspoons oil in a large nonstick skillet over medium-high heat. Gradually add spinach; sauté for 3 minutes or until spinach wilts. Remove from heat; sprinkle with remaining 1/8 teaspoon salt and remaining 1/8 teaspoon pepper. Remove fish and tomatoes from oven; discard wine. Serve fish and tomatoes over spinach.
Wine note: Flounder's delicate flavor gets a sophisticated boost from the herbal-tart character of the spinach and tomatoes. It's just the sort of dish Italians love to marry with a bone-dry Italian white wine like vermentino. With hints of wild herbs and a crisp minerally tang, vermentino is perfectly balanced for a seafood dish like this. Try Antinori Vermentino. The 2005 is about $21. -Karen MacNeil
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