Preheat a grill to 325F for indirect cooking. Add a cast iron skillet over the heat 1-2 minutes before cooking to heat up.
Add your sliced bacon and slowly cook, stirring occasionally, until caramelized and browned (about 20-25 minutes). Add your shallots and minced garlic next to brown for 2-3 minutes. Finally, add your spinach and bread crumbs. Cook until the spinach has softened and everything is mixed together thoroughly. Pull off and set to the side to cool.
Take your prime rib and begin slicing between the meat and the rib bones. Slice about ⅔ down the rib bones, then slice about 1-1.5” into the meat. Take your stuffing and add it to the sliced area that you just created. Tie the meat down with butcher twine, but not too tightly as the stuffed could be pressed out while cooking. Lather with oil and generously season with salt, pepper and garlic. Set to the side.
In a bow, mix all the ingredients for the Tangy Horseradish Sauce and set in the fridge until ready to serve.
Heat your smoker/grill for a two zone indirect fire at 250F. Add some wood chips or wood chunks if desired. Add your Stuffed Prime Rib and cook for about 25 mins per pound (about 2.5-3 hours). Once the steak has hit 115F, pull it off and let it rest for 25 minutes.
Onced one resting, remove the butcher twine and slice up your steak. Serve with the horseradish sauce and chopped chives. Enjoy!