Prepare the mussels and discard any that are open. Fry the bacon in a large pan for 5 minutes until crispy. Remove and set aside.
Add the shallots and garlic to the pan and fry gently for 5 minutes until softened. Pour in the beer, add the cabbage and bring to the boil. Season with freshly ground black pepper.
Add the mussels and bacon, then cover with a tight-fitting lid and cook for 3-5 minutes until the mussels are open. Discard any mussels that are still closed. Scatter with parsley and serve with a squeeze of lemon juice.