Slice tuna roughly 3cm thick.
Place the sesame seeds onto a tray, add the tuna chunks, turning them over in the seeds so they’re nicely coated.
Heat olive and sesame oil in a medium frying pan over a medium heat.
Peel and thinly slice the garlic and add most of it to the pan. Fry for 1 to 2 minutes, or until golden and crisp, then use a slotted spoon to transfer to a plate (don’t drain away the oil!).
Return the pan to the heat then add the sesame-coated tuna to the garlicky oil. Sear on one side for 10 to 20 seconds. Using tongs, turn the tuna over and keep cooking until you’ve seared only four sides of each chunk. Transfer to a plate.
Peel and finely grate the ginger and add to a bowl with the soy, 1 teaspoon sesame oil and the remaining sliced garlic. Add a squeeze of lemon juice, then mix well to combine.
Cut the seared tuna into slices, roughly 1cm thick
Serve sprinkled with the dressing, garlic chips, coriander leaves, spring onion, chilli and drizzled with olive oil.