Place a rack 4 inches from heat source and preheat broiler to high. Line a rimmed baking sheet with foil; mist with cooking spray.
In a small bowl, stir together Parmesan, butter, mayonnaise, lemon juice, basil, ¼ tsp. pepper, garlic powder and crushed crackers until thoroughly mixed. Place topping mix in freezer while preparing fish.
Place fillets in a single layer on baking sheet. Drizzle with olive oil and season with salt and pepper. Broil until fish is opaque, 7 to 8 minutes. Remove from oven and spread cracker mixture evenly over filets. Broil until topping is golden brown and edges of fillets are crispy, about 2 minutes. Serve with lemon wedges, if desired.