1. Firstly begin by heating up a griddle pan or frying pan until searingly hot.
2. In a pestle and mortar roughly crush the coriander seeds and peppercorns.
3. Mix in the sesame seeds, paprika and a good pinch of salt.
4. Dry the tuna steaks with a kitchen towel before rubbing the spices all over the top and bottom.
5. Drizzle the griddle pan with the vegetable oil before placing the tuna on top.
6. Leave them to cook for around 45 seconds before carefully turning over. Tuna is best served pink and so don't leave them on too long.
7. Remove and set aside whilst you finish everything off. Make ribbons out of the cucumber using a vegetable peeler, stopping when you hit the seeds.
8. In a bowl mix together the mustard, soy sauce, sesame oil, honey and lemon juice.
9. Drizzle the dressing over the cucumber and stir through the fresh coriander.
10. Slice the tuna into 1 cm thick slices and lay on a plate fanning them out. Top with some dressed cucumber and a little extra dressing if there's any left.