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, 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.