Preheat oven to 230ºC . with oven rack in center of oven.
Brush fish with glaze or other seasoning and place it in center of parchment= =2E Sprinkle lemon juice over the peppers and place them and onion slices around the fish. Wrap the edges of the paper over the fish, rolling edges tightly t= o prevent steam from escaping. Place the parchment package in an oven-proof pa= n and bake for 5-8 minutes, until fish is cooked. Remove from the oven, and pr= ick the parchment package with a sharp knife to release steam.