Minimal first:

A fish, or fillets of a fish: salmon, sea trout, haddock, cod...

Place in oven safe covered dish, flat, or rolled, if fillets.
Douse liberally with pepper and lemon juice - add a little water if dish is dry after ten minutes (usually isn't, but...)
Bake at 425F for fifteen to forty min., depending on thickness of fish, check for done-ness. Serve with boiled potatos in jackets or porato salad.

More exciting next:

Same fish...

Place in oven safe covered dish. If fillets, may be rolled with butter or other goodies inside, if whole, may be layered with onion and lemon slices, or olive oil and seasonings. If salmon, may be slathered with BBQ sauce to good effect. Proceed as previous.

My favourite fishes!

Whole haddock, eviscerated and stuffed with a savoury bread and onion stuffing, same as you'd put in a chicken, seasoned with sage, savoury, tarragon, black pepper. Bake thoroughly at 400F.

Salmon, haddock, Finnan haddie, baked as usual and swimming in hard-boiled egg sauce. Egg sauce is just a nice white sauce made with flour, butter, milk, pepper, salt, dash of lemon, into which chopped HB eggs are stirred at the end.

Salmon layered with onion, lemon, pepper, a little butter, wrapped in foil and grilled on BBQ.

Marinara sauce!

Pretend you plan on making a chowder. This means you can use any combination of white fish (haddock, cod, sole, etc.), baby clams, scallops, crab, shrimp, etc.

Saute gently in olive oil with finely chopped onion and garlic (shallots are very nice for a change), plus oregano, basil, tarragon, parsley and whatever other herbs you favour in your spaghetti. Add canned tomatos, or lots of chopped fresh ones if you have 'em. I prefer both: a couple fresh tomatos add zing to the mellowness of the canned ones, IMO.

Simmer gently until fish is nearly cooked, add tomato paste to thicken; simmer briefly again to meld flavours and complete cooking. Serve on favourite pasta.