1. Bring a pan of salted water to the boil. Drop in the noodles, cover and take off the heat. Leave to soak for 4 minutes.
2. Meanwhile, heat a frying pan over a high heat until quite hot. Add the oil and tuna steaks and sear over a high heat for 30 seconds on each side.
3. Take the pan off the heat and add the soy sauce and balsamic vinegar. Simmer on low heat for 2 minutes. Turn the steaks over (be careful not to splash yourself!), sprinkle with the garlic, ginger and chilli and simmer for a further 1 minute.
4. Place the tuna on 4 warmed plates, spoon over the sauce and pile the spring onion shreds on top of each steak. Drain the noodles, tip them into a serving bowl and toss with the sesame oil. Serve with the tuna.