Using lemon butter with pepper added should work. It's the same thing as the spice
Put it on the fish in a baking dish. (Use one that is at least an inch deep so you can put water in with the fish.) Once you have the fish laying in the pan, cover it with water and add the lemon butter and pepper. If you have aluminum foil, cover it and place in 400 degree oven for 50 minutes.
The potato in the microwave sounds good.
Let me know if you need any more help.