Hi, OP -
I second a PP’s idea of ginger paste. Some of it is very good. Also a good store bought pesto, if it is possible to find one without garlic. Or you could make some and freeze it in portions, although I know that is batch cooking. But it is the basis for many good, easy toppings for fish and chicken.
Also, Baked Fish with Vegetables -not a tray bake, but similar. A method that can be adapted to Eastern or Western flavours.
Can you use butter, cultured butter or clarified butter? Many with dairy intolerance are OK with the latter. An oil suitable to the flavourings is also good.
Generously grease a pan large enough to hold your fish fillets, and at least 5 cm deep.
Cut/slice your choice of veg into serving pieces. If some need more cooking time than others, microwave them. Potatoes, carrots and fennel seem to me to belong to this category.
If using potato slices, line the bottom of the greased pan. Toss the rest of the veg with a liberal amount of suitable oil and/or small pieces of butter, salt and pepper, and fresh or dried herbs.
Keep it easy. Eg. A layer of zapped potatoes on butter, S and P, tossed slices of leeks and carrots and whole haricots verts. Branches of fresh thyme, don’t bother stripping them.
Douse lightly in white wine of choice and bake until veg are about 15 min from finished. Plop greased, seasoned fish fillets skin side up on top and finish cooking.
I set the oven at 180C for this. Others will want to experiment. The butter or oil, white wine and fish juice make a nice sauce.
Serve with an appropriate carb.
Many versions are possible. I just realised one could use sake or sherry in Asian versions.