Remove the roots and clean the spring onions, retaining as much of the green leaves as possible, then chop them quite finely. Peel the potatoes and cut into smallish chunks. Peel and chop the garlic.
Heat the oil in the cooker over a medium heat then add the garlic. Stir to soften then lower the heat, add the spring onions and sauté for about 5 minutes.
Put in the potatoes and stock, and bring to the boil. Cook under pressure for 8-10 minutes then cool under running water.
Stir in the soy sauce & oregano, then use a hand held blender to mix to a smooth consistency. Simmer and stir in the open pan for another 5 minutes adding a little more stock if you prefer a thinner soup.
Scatter some fresh herbs over each portion, if you wish, and serve with chunky bread.