Scrape and clean the fish.
Light a BBQ grill. Cut up the leeks and boil them in lightly salted water for 5-6 minutes. Grill the peppers until black spots start to appear all over the skin. Lay them in a plastic bag, tie up the bag and allow them to steam while cooling down. Remove the skin and seeds.
Sprinkle the chilli and salt on the fish. Make a few incisions in the skin. Place a few lemon slices in the belly. Grill the fish with the leeks. The fish will be ready once the meat has been warmed through and flakes away when you prick it with a fork.
Serve the fish with the leeks and peppers.