Heat the oil in a large skillet over medium-high heat. Brown the pork cubes in two batches, then transfer them to the slow cooker.
Lower the heat to medium and add the onion to the same skillet. Cook for 4 minutes until softened, then stir in the garlic for 30 seconds.
Pour the stout into the skillet and scrape up the browned bits. Add this mixture to the slow cooker along with the beef broth, bay leaves, thyme, salt, and pepper.
Cover and cook on low for 6 hours.
Stir in the parsnips and continue cooking for 2 more hours.
Add the cabbage for the final 45 minutes of cooking.
Remove the bay leaves, taste for seasoning, and sprinkle with parsley before serving.