Prepare slow cooker liner with nonstick cooking spray. Place the ham into the slow cooker with the cut side facing down. Pour the soda over the ham. Mix together the brown sugar and the mustard.
Brush the brown sugar mixture over the ham. Cover slow cooker with the lid or if the ham is too large, wrap the top of the slow cooker with aluminum foil.
Cook on low for 4 to 6 hours or until the ham is warmed through to the center to your liking.
** Oven directions ** Preheat the oven to 350 degrees. Place the ham into a roasting pan. Pour the soda over the ham. Mix together the brown sugar and the mustard. Brush the brown sugar mixture over the ham. Cover the ham and bake for 90 minutes. Uncover and baste well. Continue baking for 30 minutes.