Baked Pangasius with Cream Sauce

So I know that I was attempting to eat healthy (go away, thunder thighs!!!) But I'm trying to introduce the boyfriend to fish. It's healthy, and I love it, and if you buy it here frozen, it's actually quite cheap and delicious. I also just got back from London, where I bought some absolutely lovely cheddar. So the other day I made this dish, and it was super easy and quick (with a bit of help)

Baked Pangasius with Cream Sauce

1 400g fillet of pangasius, frozen or fresh. (Pretty much any whitefish will do)
1 small onion
2 cloves garlic
150-200 ml heavy cream (you could sub light cream, but all I had was heavy)
1 tablespoon mustard
1/2 c. (120 g) grated cheddar cheese
Salt and pepper to taste

Rinse fish and pat dry
Place in baking pan
Sprinkle with salt and pepper
Bake at 350 F (175 c) for about 10 minutes, until fish flakes with a fork

While the fish is baking, make the sauce.

Process the onion and garlic in a processor
heat a bit of oil or fat in a pan sautee the onion and garlic until fragrant
pour in the cream and add the mustard
simmer gently
Add the cheese, and stir til the cheese melts
salt and pepper to taste

When the fish is done, pour the sauce over the fish. Serve with rice or veggies or potatoes