Spray a 4 quart slow cooker with nonstick cooking spray.
In a medium mixing bowl, stir together the gingerbread mix, half and half, cinnamon and ginger and raisins until moistened. The batter will be very thick. Spread the batter evenly over the bottom of the slow cooker.
In a medium saucepan over medium high heat, stir together the water, brown sugar, butter and vanilla. Bring mixture to a boil and carefully pour over the batter in the slow cooker.
Set the slow cooker on the high heat setting and cover. Cook for 2 hours (the center will still appear very moist and a pudding like consistency). Remove the liner from the slow cooker or just turn the cooker off and allow to stand, uncovered, for an additional 45 minutes. Cake will be slightly cooled. Serve a spoon full of warm cake and pudding like center in a beautiful dessert bowl and top with a scoop of vanilla bean ice cream or whipped cream and sprinkle of chopped candied ginger.