Put the sugar snap peas and courgettes on a large piece of oiled foil, sprinkle with the lemon rind and plenty of seasoning then top with the fish. Drizzle with lemon juice and sprinkle with a little extra seasoning. Seal the edges of the foil to make an air-tight parcel. Chill until required.
Beat the olives with the butter and half the basil. Season with pepper, then spoon on to a piece of greaseproof paper. Wrap tightly and roll into a small log shape. Chill until required.
When ready to serve, put the fish parcel in a grill pan, open the foil and top the fish with 4 slices of olive butter. Cook under a preheated hot grill for 8–10 minutes until the fish is browned and flakes when pressed with a knife. Lift out the fish and cook the vegetables for a few minutes more, until just tender and lightly browned.
Spoon the vegetables on to serving plates and top with the fish fillets and any pan juices. Top with the remaining butter, cut into thin slices, and garnish with the remaining basil.