Give 5 sprays of the low fat cooking spray in the bottom of a large saucepan which is big enough to hold 2.5 litres water in total. Or add the olive oil.
Heat the oil in the saucepan until it is hot and turn the temperature down to medium.
Add the diced onions, diced carrots and diced ham and sweat them down until they are soft it will probably take 8 minutes or so, if using the cooking spray method, quicker if using olive oil. Keep stirring the vegetables around the pan so that the ham also does not burn.
Once the onions and carrots are soft add all of the pre-soaked yellow split peas, mix together, and then add the 1.5 litres of chicken stock and the bay leaf.
Simmer for about 1 hour until all of the vegetable mixture is soft. You will need to keep stirring the pot to remove the bubbles on top.
Switch off the heat and allow the soup to cool for half an hour.
Remove the bay leaf.
Puree the soup in batches and put back in a saucepan, gently re-heating the soup.
Season with salt and pepper to taste.
Allow to cool a little serve garnished with parsley.
Or portion the soup into individual containers with labels on, and freeze to be used when required.