Slice onions and celery, this is How to Cut Cabbage into the size of pieces you want (smaller will be very tender, I suggest 1.5"x1.5" pieces. Add into the slow cooker with frozen mixed vegetables.
Pour in chicken broth and water. Cover and cook for 7-8 hours on low or until ingredients are as tender as you'd like them to be.
Add salt and pepper to taste and serve with a sprinkle of parmesan cheese on top if desired.