Score ham with sharp paring knife and place cut side down in the slow cooker. Add orange juice to the bottom of the pan.

In a small bowl, combine butter, brown sugar, cinnamon, allspice and dijon mustard. Stir to combine. 

Use a basting brush to brush 1/2 of the brown sugar mixture all over the ham - reserve the remaining glaze for later. 

Cover slow cooker and set to LOW. 

Let cook until internal temperature reaches 140 degrees F. at it's thickest point (approx. 4-5 hours, may take longer depending upon how big the bone is - will take less time if it is a boneless ham). With 10-15 minutes remaining on the cook time, brush on the remaining half of the glaze and cover until done. 

Remove and let the fully cooked ham rest 10 minutes. Alternatively, you can put in the oven under the broiler for a few minutes to make the glaze more tacky and the outside more crispy, but this is not required - up to personal preference.

Slice and serve- enjoy!