Mix the yeast and milk and leave in a warm place until the mixture begins to froth. Stir in the oil. Combine the flour and salt in a mixing bowl.
Make a well in the centre of the flour mixture and add the yeast mixture. Working from the sides, gradually mix the flour and liquid to make soft, sticky dough.
Knead for 7 minutes or until the dough is very elastic and springy to the touch. Cover and leave in a warm place to rise for 1-2 hours or until doubled in size.
Knock back gently and shape into a ball. Press or roll the dough into a rectangle. Mix the walnuts and onions and scatter evenly over the dough.
Roll up the dough, cover it and leave to rise for 30 minutes. Shape the dough into a long oval and put it on a greased baking sheet. Leave to rise for 30 minutes.
Meanwhile preheat the oven to 200°C. Score the top of the bread and bake for 30-35 minutes or until done. Serve with mature Cheddar cheese.