Sprinkle Cajun seasoning on both sides of fillets; lightly coat fish with cooking spray. Arrange fish in a wire grilling basket coated with cooking spray. Place basket on grill rack; cover and grill 5 minutes. Turn grill basket over; drizzle lemon juice over fish. Cover and grill 5 minutes or until fish flakes easily when tested with a fork. Serve with grilled lemon slices, if desired.