Tofu broad bean, lemon & garlic stir-fry

Ingredients: Bout 3-4 tbsps toasted sesame oil 300g/10 ½ oz/2 ½ cups firm tofu, cut into bite sized cubes 1 bunch spring onions/ scallions, trimmed and sliced diagonal 4 garlic cloves, finely sliced into silvers 5cm/1 ¾ in pieces fresh root ginger, peeled and finely sliced in silvers ½ lemon grass stalk, finely chopped 1