How to cook mild white fish

 (not oily fish like salmon) is to bake (or microwave) it with chopped onions and tomatoes on top and around it. (I pre-nuke my tomatoes/onions, then pour over fish fillets in an oven safe dish, cover, then bake at 400 F for about 12-15 min.)
You can do the same thing with salsas of all types... I like fresh pico de gallo, but anything should work.
Many fish can also be cooked "en papillote" (in an aluminum foil or parchment "pouch") in the oven, or microwave, or on coals. There are loads of flavorings and veggies, etc., you can toss onto the fish before closing the pouch too:
easy….any fish… ( skillet)
…melt a little butter (or oil) in the skillet
....sprinkle about 1-1/2 tsp cajun spice into butter (or use any other "spice mix")
…place the fish into seasoned butter/oil….cook about 3 mins on each side till golden brown.

…then add about 3/4 c. water…cover and steam fish till flakes
Onion, celery, bread crumbs Stuffed Fish (6)
(or use Stouffers various stuffings ….or Italian bread crumbs?)
Cut fish into strips. Line well-greased muffin tins with fish strips; sprinkle with salt.
In a small skillet, saute onion and celery in butter until just tender.

.Combine vegetable butter mixture with 1 teaspoon salt, pepper, sage, and bread cubes.
Add a little hot water if stuffing seems too dry.

Dot the top of each stuffing center with a little butter then sprinkle with chopped parsley.
Bake at 350° for 30 minutes, or until fish flakes easily with a fork.