Place a large non-stick frying pan on a medium-high heat. Rub the miso all over the tuna, then pat on the sesame seeds to cover. Place in the hot pan with 1 tablespoon of olive oil and sear for 1½ minutes on each side, so it’s beautifully golden on the outside but blushing in the middle. Remove to a board to rest. Quickly wipe out the pan with a ball of kitchen paper, then return to the heat.
Trim the spring onions and slice at an angle the same length as the sugar snaps, tossing both into the hot pan with a few drips of red wine vinegar and a pinch of sea salt for 2 minutes to lightly catch and char. Slice the sesame tuna and serve on top of the veg, drizzled with 1 teaspoon of extra virgin olive oil.