Coat corn ears with cooking spray. Place 1 cup tomatoes, 1 tablespoon oil, and shallots in a bowl; toss to coat. Place tomato mixture in a grill basket. Add corn to grill; cook 6 minutes or until lightly charred, turning occasionally. Add tomato mixture to grill; cook 4 minutes or until tomatoes blister and turn lightly brown. Remove corn kernels from ears; discard cobs. Coarsely chop shallots; set aside. Place grilled tomatoes, remaining 1 tablespoon oil, 1/4 teaspoon salt, and 1/4 teaspoon pepper in a food processor; process until smooth.
Coat fillets with cooking spray; sprinkle with 1/2 teaspoon salt and 1/4 teaspoon pepper. Add fillets to grill; cook 3 minutes on each side or until desired doneness. Remove; keep warm.
Slice remaining 2 cups tomatoes in half. Combine corn, shallots, fresh tomatoes, 2 tablespoons pureed tomato mixture, remaining 1/4 teaspoon salt, and remaining 1/4 teaspoon pepper in a bowl. Place 1 cup corn mixture on each of 4 plates. Top each serving with 1 fillet, 1 tablespoon pureed tomato mixture, and 1/2 teaspoon balsamic glaze. Top with basil, if desired.