Brush the fillets with oil on both sides, season with Cajun seasoning to taste then place into a 20x30cm baking dish.
Bake in the preheated oven until the flesh is no longer translucent and the fish flakes easily with a fork, about 10 minutes.
Meanwhile melt the butter in a small saucepan over medium heat. Stir in the garlic and cook until the garlic has softened and the aroma has mellowed, about 2 minutes. Stir in the Alfredo sauce and bring to a simmer. Reduce the heat to low and keep warm until the fish is ready. Pour the sauce over the fish to serve. Sprinkle with additional seasoning if desired.