Carefully remove the ham from its packaging. If it's a spiral-cut ham, it's ready to go. Place the ham cut-side down (if applicable) or flat into your 6-8 quart slow cooker.

In a large mixing bowl, whisk together the maple syrup, Dijon mustard, brown sugar, apple cider vinegar, garlic powder, and black pepper until well combined and the brown sugar has dissolved.

Pour the maple Dijon glaze evenly over the ham in the slow cooker, making sure to coat as much of the surface as possible. If spiral-cut, try to let some of the glaze seep between the slices.

Cover the slow cooker and cook on LOW for 3-4 hours, or until the ham is thoroughly heated through and tender. If using a meat thermometer, the internal temperature should reach 140°F (60°C). Baste the ham with the glaze from the bottom of the slow cooker every hour or so, if desired.

Carefully remove the ham from the slow cooker to a large cutting board or serving platter. You can spoon additional glaze from the slow cooker over the ham before serving. Let it rest for 10-15 minutes before carving and serving.