Combine first 5 ingredients. Stir with a whisk until smooth and creamy. Cover and chill at least 1 hour.
Heat oil in a large nonstick skillet over medium-high heat. Sprinkle fillets on each side with 1 teaspoon salt. Place fillets in pan and cook 3 minutes on each side or until fish flakes easily when tested with a fork. Serve with wasabi mayonnaise.