If I had these ingredients, I would see what veg I had also like brocolli, or fine beans or sweetcorn etc, make a cheese sauce and mix with the veg and fish, slice the potato very thinly layering up the fish combined with the veg and cheese sauce (and potato slices?), and then veg etc etc, then top it off with some tattie slices then maybe a sprinkling of cheese - put in the oven to brown.
Start by roasting some patatoes...season them with some basil,thyme and oregano..plus salt and pepper. When almost done add thinly sliced red onions,chunks of tomato and your fish....drizzle some olive oil over and bake til the fish is done-abot 10-12 minutes.