Combine gluten and nutritional yeast in a large bowl. In a separate bowl, mix together water, soy sauce, ketchup, garlic, lemon zest and spices.
Pour the wet ingredients into the dry and combine. Knead dough in the bowl for about 3 minutes until you have a spongy dough. Let rest for a few minutes, then shape into a log about 7 or 8 inches long. Cut into 3 pieces.
Put the cold water and soy sauce in a large saucepan and gently put the pieces of dough in the liquid. Partially cover the pot and bring to a boil. Lower heat and simmer for one hour, turning the pieces occasionally. Let it cool for ten minutes, then remove the seitan.
Wrap each piece in plastic wrap or place in a zip lock bag and refrigerate for several hours or overnight.
Start a fire in your smoker. Soak wood chips (preferably hickory) for 45 minutes or more. Coat the seitan pieces in the dry rub mixture and put it on a grill basket or right on the grate. Throw some wood chips on the hot coals and close the cover. Smoke for 1 ½ hours, adding more soaked wood chips occasionally.
Whisk the sauce ingredients together until sugar dissolves. Let the smoked seitan cool for 5 minutes, then slice, drizzle with sauce and serve plain or on buns.
