Lay a sheet of filo pastry on a wooden board, brush with Dijon Mustard and season to taste. Place a tuna loin along the side of the filo pastry and begin to roll the tuna, encasing it in the pastry. When you reach the end, brush the sides with a little water and stick it together. Repeat with the remaining pastry and tuna.
Heat a frying pan with a drizzle of olive oil. Fry each side of the tuna filo roll very quickly until golden brown. Once brown, remove and place on piece of kitchen paper to soak up any excess oil.
To serve, cut the ends off the tuna filo roll and cut the roll again in half. Cut each half diagonally and present on plate.
It is even more delicious when combined with mustard ice cream (see recipe on this site). Garnish with a herb salad (eg small shoots of coriander, chives, chervil, dill, red amaranth, drizzled with olive oil and a pinch of sea salt).