For spring onion curls, cut the onions in 10cm (4 inches) in lengths then thinly slice them into strips. Alternatively, slice the spring onions diagonally. Place the cut onions in a bowl of cold water and it set aside.
In a small bowl combine soy sauce, mirin, sake and sugar and mix well to combine, set aside.
Place the tofu on a chopping board. Using paper towels and hands gently but firmly press on the tofu to release any excess water. Cut the tofu into 1cm slices and again in half, repeat with the gentle press and use paper towels to blot off any water.
Place the flour in a plate and dust each slice of tofu in the flour and shake off any excess flour. For a quick method, use a large snap bag, place the flour and tofu inside, create some air and shake bag to coat the tofu.
To deep-fry, preheat the oil to 180°C (360°F) and cook tofu for 2 to 3 minutes making sure to turn the tofu so it cooks evenly. For pan-fried tofu, pour the oil in a frypan until it coats the entire surface of the pan. Heat the oil on medium to high heat and cook the tofu on each side for 3 to 4 minutes or until golden. Transfer the tofu on to a cooling rack.
Remove any excess oil remaining in the pan or use a different frypan. On medium to high heat add in the teriyaki sauce mixture and stir until mixture bubbles. Add in the tofu and gently stir it into the sauce making sure to coat each side evenly. The tofu is ready once the sauce has thickened and the tofu has caramelised.