1. You can use other white meat fish fillets such as snapper, cod, jewfish, bream. The fillets should have skin on, so that it adds to the colour to the dish.
You could serve a larger portion of fish if you like.Just increase the amount of konbu and sake accordingly.
2. You could use other vegetables suitable for steaming. Beans, snow peas, shiitake mushrooms, asparagus might be good. The amount of vegetables can also vary but you need to think about the balance against the size of the fish fillet.
In my view, mushy vegetables such as potatoes, pumpkins are not best suited for this dish, nor vegetables with strong flavours such as capsicum.
Depending on the colour of the fish, you may want to change the choice of vegetables. For example, if you are steaming cod, you may add sliced carrots to add a bright colour to the dish. If you cut the carrots into flower shapes as explained in my post, Sanshoku Bento, it would look pretty.
3. If each stem is small, you may take a couple of stems together as one.
4. Please refer to the recipe to make ponzu in Japanese Dressings. I would strongly recommend that you make it at home. Ponzu can keep a long time in the fridge. The longer you keep it the better the flavour gets.
But if you wish, you can buy a bottle of ponzu from Japanese/Asian grocery stores.
5. The time taken to cook the fish fillets will depend on the strength of the steaming as well as the thickness of the fillet. My fish was about 1.5-2cm (5/8-3/4”) thick and steam was on high.
6. The sake liquid from cooking contains tons of flavour with the konbu and fish so don’t discard. But you might find that you would only need half of what’s left on the steaming plate.