- Mix the tuna, pepper, celery, fromage frais and pesto together.
- Cook the gnocchi in plenty of boiling salted water until it bobs to the surface of the water. Drain well and return to the saucepan. Stir in the tuna mixture, season to taste.
- Spoon the mixture into a large gratin dish and sprinkle with the Parmesan cheese. Bake in the oven for 30 minutes or until the gratin is piping hot and golden brown. Cool for a few minutes before serving.