Preheat the oven to 220C, gas mark 8. Cut out 4 large heart shapes using greaseproof paper. Arrange the potatoes and peas on one half of a large sheet of good quality greaseproof paper. Put the hake fillet on top with the asparagus.
Put a slice of butter on top of the fish and a couple of lemon wedges. Sprinkle the fresh and roughly chopped mint over the top. Seal the parcel thoroughly.
Arrange the fish on the baking sheet. Cook for 10 minutes and the serve the parcel directly to your guest.