Using a large knife roughly chop the tomatoes, onions and red pepper. Mix together in a bowl and add the sweet chilli sauce — enough to give the heat that you like.
Crush the peppercorns coarsely with a pestle and mortar — or use the end of a rolling pin in a small bowl. Sieve to remove the fine pepper — you can use this to season other meals.
Place the coarsely crushed pepper on a plate and roll the sides of the tuna in the peppercorns.
Heat the oil in a nonstick pan. When hot, add the tuna and cook for about 1-2 minutes on each side. Tuna should be served rare as it becomes very dry if over-cooked. Serve with salsa and salad leaves.
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