Prepare all the ingredients
Cut the potato in pieces and preheat oven to 200C degrees
Spread the oil with a piece of potato over the tray
Cover the tray with the rest of pieces and season with salt or whatever you want. Put inside the oven for 8'
While you can cut the onion and pepper
After the 8' cooking the potatoes, put the onion and pepper for 8' more.
After the last 8' put the fish over the onion & pepper and cover with a little of oil (just one or two spoon of oil). Cook until fish is done (you can use 15'-20' as average time)
Fish is done. You've to clean only the tray. Cooking in oven is quickly, easy and clean.