In a frypan over a medium-high heat, heat the olive oil. Season the steak pieces with salt and pepper, and add to the fry pan. Cook on all sides until all the steak is browned on the outside (you may need to remove excess liquid from the pan). This should take about 10 minutes. 

Remove the steak from the pan and place in the slow cooker. Maintaining the heat in the fry pan, add the onion, carrots and celery and cook for about 3-4 minutes, stirring occasionally and adding olive oil if sticking occurs. 

Add the onion, carrots and celery to the slow cooker once the onion is browned and the carrots and celery begin to soften. Add the red wine to the fry pan and allow to simmer for a minute, ensuring you use a spoon to scrape off any caramelised bits from the pan. Pour the red wine into the slow cooker and remove the fry pan from the heat. 

Add the garlic, bay leaves, fresh thyme, tomato paste and beef stock to the slow cooker and stir to combine. Place the slow cooker on a low heat for 8 hours. 

An hour before serving, add the chopped mushrooms to the slow cooker and stir. 

When you are ready to serve, spoon the mixture over pasta or polenta, or greens if you wish, and sprinkle with fresh parsley.