Heat the oil in a large pot or Dutch oven over medium heat. Add the onions and carrots and sauté for 5-8 minutes, or until the onions are starting to brown. Stir in the garlic and cook for a further 1-2 minutes. Pour in the chicken stock and bring to a gentle simmer. Add the pork shank to the pot, cover, and simmer for 1 hour 30 minutes. Check occasionally and top up with water as needed to maintain the liquid level. Stir in the soaked split peas and continue to cook, covered, for an additional 45 minutes, or until the peas are tender and beginning to break down into a thick, soupy base. Stir occasionally to prevent catching on the bottom. Season to taste with salt and pepper. Remove the shank from the pot, slice or shred the meat from the bone, and return it to the soup. Discard the bone and optionally reserve some pork to use as a garnish.
Ladle the soup into bowls, top with the reserved pork if using, and scatter over the chopped parsley. Serve immediately with fresh bread.