Heat oven 400F. Spoon 2 tablespoons of lemongrass basil sauce over fish fillets spreading over all sides; let marinate for 15 minutes. Meanwhile, blanch green beans in boiling water until crisp tender and then drain and shock in ice cold water to retain green color; set aside. Mix salt and white pepper together; sprinkle evenly over fish fillets. Spread sesame seeds over a flat plate. Whisk cornstarch and water together in a bowl until incorporated. Spoon the cornstarch mixture over the fish, turning, to thinly coat both sides. Press fish fillets, 1 at a time, into the sesame seeds coating both sides. Heat oil for shallow frying in an oven-safe skillet over medium-high heat. Cook fish, turning once, for 2 to 3 minutes per side or until sesame seeds are lightly brown. Transfer skillet to oven and roast for 5 to 8 minutes or until fish is cooked through. Meanwhile, heat 1 tablespoon of oil in another skillet over medium heat. Add the beans and tomatoes; cook 2 minutes. Add remaining sauce and cook until heated through. To serve: arrange beans and tomatoes in center of each of 4 plates. Top each with a fish fillet. Spoon some sauce over fish and garnish with fresh basil.