Finely chop the mushrooms in a food processor (or chop them by hand). Transfer to a large bowl. Add the breadcrumbs, paprika, and salt and mix to combine. Add the egg and turkey and gently knead to incorporate. Transfer the meat mixture to the prepared slow cooker, pressing out to the edge of the insert and mounding slightly into a domed loaf shape. Cover and cook for 4 hours on the low setting. Unplug the slow cooker.