Skin the tuna and cut away the dark bloody bits. Rinse and dry. Chop the anchovy, mint and garlic finely, then mix them together. With the point of a knife make incisions in the tuna 6 cm apart and 3 cm deep; fill these incisions with the chopped mix.
Rub olive oil, salt and pepper over the tuna, and put in a roasting dish that is just big enough to hold it with the tinned tomato pieces and their juice. Scatter the red onion over and about it, and put in the oven with possibly a little more oil on top.
Serve the tuna warm with roast cubed potatoes. Spoon the onions and juice over.
© 1996 Alastair Little. All rights reserved.