Using a mortar and pestle, finely crush the fennel seeds, mustard seeds and peppercorns. Add the sea salt and all the other ingredients up to and including the ground cardamom, mix well.
Melon & radish salad
Pour the balsamic and oil into a large bowl, season, mix well. Add the chilli pepper, melon and radish, mix.
Toss the tuna in the spice mix. Heat the oil in a non-stick frying pan. Fry the tuna steaks in batches for approx. 1 min. on each side.
Remove and drain on paper towels.
Serve the tuna with the melon & radish salad and fresh coriander.