Preheat the grill to hot.
Grill the peppers, turning frequently, until the skin is blistered and turning black. Remove from the grill and transfer to a plastic bag. Tie well and leave to one side for 15 minutes.
Meanwhile, beat together the cream cheese and the fromage frais until smooth. Once the peppers are cool, remove from the bag and peel away the skins. Spread the cream cheese and fromage frais mixture onto the base of the peppers, filling them half full with the mixture.
Spoon the flaked tuna carefully on top, then garnish with slices of red onion and parsley leaves on top of the tun.
Prick with wooden skewers to hold in place. Garnish with sprigs of parsley leaves before serving.