Preheat a smoker to 250 degrees F (120 degrees C). Add a few chunks of applewood.
Trim excess fat from leg of lamb.
Apply a thin layer of yellow mustard all over the leg of lamb to make it easier for the rub to stick. Apply a medium coating of rub until the meat is completely covered and cannot be seen through the rub.
Add the lamb to the preheated smoker. Check after a couple of hours to see if the bark has formed. If it has not, check back every 30 minutes until the bark is set.
After the bark is set, wrap the lamb in foil with some mopping liquid such as beer, chicken stock, or red wine.
Cook the foil pouch in the smoker and probe the meat through the foil until it feels tender when you probe it. Approximately 4 hours.Tip: The internal temperature when done is between 175 to 195 degrees F (80 to 90 degrees C). Don’t rely on the temperature reading alone, but also on the feel of the meat when you push the probe in.
Remove the lamb and cut open the foil to let it cool and then shred the lamb into chunks.
Heat the canola oil in a saute pan over medium heat. Add the diced onions, celery, and carrots. Cook until the vegetables are tender, about 5 minutes.
Add the rosemary, garlic, tomato paste, Worcestershire, BBQ sauce, and chicken stock. Mix well and heat until boiling.
Add the shredded BBQ lamb. If the mixture is dry, add more red wine or chicken stock. The mixture of lamb and vegetables should be a bit soupy. Season to taste with salt and black pepper.
Preheat the camp oven to 400 degrees F (205 degrees C).
Transfer the mixture to a casserole dish or Dutch oven.
Top with mashed potatoes. Paint the top of the mashed potatoes with the beaten egg wash and sprinkle with the Parmesan cheese. Use a fork to make stiff peaks.
Bake for 20 to 25 minutes in the oven until the crust is browned.