Pre-heat oven to Gas 4, 180°C, fan 160°C.
Flake tuna into a small, shallow ovenproof dish. The lid of a small Pyrex casserole is perfect.
Pour beaten egg over tuna.
Crunch the crisps and sprinkle over the egg. Top with the grated cheese and Parmesan.
Put in oven for 15-20 minutes until bubbling and golden.
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