1. Heat a large nonstick skillet over medium-high heat. Sprinkle fillets evenly with 1/2 teaspoon salt and 1/4 teaspoon pepper. Coat pan with cooking spray. Add fillets to pan; cook 3 minutes or until browned. Turn fillets over; cook 4 minutes or until desired degree of doneness. Remove fish from pan; loosely cover, and keep warm. Wipe pan clean with paper towels.
2. While fish cooks, place vinegar in a medium bowl. Gradually add oil, stirring with a whisk. Stir in shallots.
3. Return pan to medium-high heat. Add tomatoes, remaining 1/4 teaspoon salt, and remaining 1/4 teaspoon black pepper; sauté for 3 minutes or until tomatoes soften. Add tomatoes to vinaigrette; toss to combine.
4. Arrange 1 1/4 cups arugula on each of 4 plates; top each serving with 1 fillet. Spoon about 1/2 cup tomato mixture over each salad, and sprinkle with 1 1/2 teaspoons nuts.