Repurposing tasteless fish

your ideas sound very good,I am thinking lemon,parsley,salt and pepper in melted butter and olive oil.Halibut is probably the mildest tasting fish and if a super fresh quaity, you would enjoy the sweetness and good texture and freshness quality

And then there's the eternally delightful and perfect-for-brightening-up-just-about-anything sauce gribiche! Flake the fish, stir in more sauce gribiche than you think it needs and make a sandwich on brioche, or perhaps whatever you'd use for a lobster roll, with a few ribbons of radicchio to make it interesting. ;o)

So what did you do with the fish>? hopefully you ate it by now, its' getting a little old.

Or make fish salpicón - chop scallions, chilies if you like them, cilantro leaves; I also add parsley, though it's not traditional. Whisk up a quick dressing of orange juice (I use a teaspoon of frozen concentrate - see John McPhee's long-read in the New Yorker for more information on why that's a great idea), juice of a lime, salt, pepper, olive oil. Flake the fish in a bowl with the dressing and chopped aromatics and herbs. Test for salt, pepper, lime juice.

Serve on a large tortilla that's been heated until crisp (tostada) or in smaller ones (tacos) or, when summer tomatoes are at their best, remove the calyx and core, and stuff with the salpicón. Fresh corn in season is also a nice touch, especially when tomatoes are involved. ;o)

Halibut Roll (like lobstah roll but, you know)

How about fish croquettes or cakes? Mix with some crushed saltines, herbs or spices and little mayo. Coat with some panko and fry or bake.

Another variation on the taco theme . . . . sweat a chopped onion with garlic in a bit of oil; when the onion is soft, add generous pinches of ground cumin, allspice and black pepper (and chili, if you like) and saute until the spices are fragrant. Add a bit more oil and some chopped cilantro stems. Toss the fish in and gently break up while integrating the ingredients in the pan. Put into toasted corn tortillas with pickled red onion (preferably ones made with oregano and cumin), avocado, cilantro leaves and arugula. Drizzle generously with lime "crema"- in our case, thick yogurt + the juice of a lime + salt. ;o)

The first choice for several billion people on this planet would be fried rice.

Blend or mash with soft cheese(s), minced shallots/garlic, fresh herbs, salt, pepper, and a tish hot sauce for a fish spread. Serve on crostini/crackers or fill an omelet.

I like creamtea's idea. I like the whole taco vibe. you can get a lot of flavor that way. toss in a pan with some spices and top with fresh salsa, cilantro and you are good to go. Can't waste that Halibut , not at $25.00 lb.

Lime juice, good olive oil, garlic minced with a pinch of salt, red pepper flakes, confetti of colored bell peppers, olive oil and finely minced cilantro; flake or dice the fish, toss with the above for a "ceviche" type cold salad over butter lettuce or in tacos. This is based on a Gourmet recipe from way back for "Portuguese marinated scallops" from Provincetown.

There is an article on this site from a couple of years ago that might give you inspiration:
https://food52.com/blog/10137-how-to-use-leftover-fish

Make it into a salad, a la Waldorf or whitefish, and spoon over lettuce or fill sandwiches.
Add crunch (celerey, fennel, apple and/or cucumber)
Add smooth & creamy (mayo, sour cream and/or yogurt)
Add seasoning and garnish (salt & pepper, grapes, walnuts, parsley, dill)

What did you season it with in the first place? "Tasteless Halibut" is an oxymoron in my kitchen!