1. Cook peas, covered, in boiling salted water to cover 20 minutes or until tender. Remove peas from heat, and let stand, covered, 10 minutes. Drain and rinse with cold water. Combine cooked peas, tomatoes, bell peppers, and onion in a large bowl.
2. Whisk together vinegar, Creole mustard, 1/2 cup oil, 1/4 tsp. salt, and 1/4 tsp. pepper. Stir 1/2 cup vinaigrette into pea mixture, reserving remaining vinaigrette. Cover and chill pea mixture 1 1/2 to 24 hours.
3. Rub both sides of fillets with 1 Tbsp. oil; sprinkle with remaining 1/4 tsp. each salt and pepper. Press thyme and 1 Tbsp. basil leaves onto flesh side of fish.
4. Heat remaining 3 Tbsp. oil in a large nonstick skillet over medium heat. Place fish, flesh sides down, in hot oil; cook 3 minutes or until golden. (Do not allow herbs to burn.) Turn fish; cook 4 minutes or just until fish flakes with a fork.
5. Stir arugula and remaining 1 Tbsp. basil into pea salad; divide salad among 4 plates. Top each with a fish fillet. Serve with pickled okra, lemon halves, and remaining 1/4 cup vinaigrette.