Preheat oven to 450°F. Spray rimmed baking sheet with nonstick spray.
Mix walnuts, panko, and all herbs in small bowl; sprinkle with salt and pepper.
Brush each fish fillet with 1 tablespoon melted butter; sprinkle with salt and pepper. Place fish on prepared baking sheet. Sprinkle panko-herb mixture atop fish, dividing equally and pressing to adhere.
Roast fish until just opaque in center, about 8 minutes. If crisper topping desired, preheat broiler and broil fish about 1 minute, watching carefully to prevent burning.
Transfer fish to plates; garnish with lemon wedges.