Heat some vegetable oil in a frying pan, over moderate heat.
In a large bowl, mix together the cheese, breadcrumbs and leek or spring onions.
Stir in the yogurt, herbs, mustard and salt and pepper.
Mix well until a cohesive mixture is formed. Add a little water if the mixture is a bit crumbly, more breadcrumbs if too wet. The mixture should be moist but not sticky.
Pour your soy milk in a shallow dish and the breadcrumbs into a second shallow dish.
Form mixture into 6-8 small sausages, dipping each into the soy milk and then into the reserved breadcrumbs.
Shallow fry them until they are golden on each side, about 5-7 minutes, and the middle is melting.