This recipe starts with seitan.  You can either make you own like this one, or buy some from a store. 
You want to start by finely chopping and onion and a green pepper.  Mince the garlic unless you're using the wonderful pre-minced jar of garlic.   
Heat up a large splash of oil in a heavy skillet (cast iron works great) over a medium-high heat. 
saute the onions, garlic and pepper until the onions are clear.  and starting to get a little brown. 
While the veggies are sauteing, shred the seitan with either a food processor, or just by chopping it finely with a knife. 
Once the veggie mix is ready (slightly browning) mix in the shredded seitan. 
Let this heat up for a few minutes and then add the barbecue sauce.  This is not an exact science, just pour it in from the bottle and mix well.  Once everything looks like it is coated, you've put in enough sauce. 
I've found that the best flavor for this comes from letting the sauce burn on the bottom of the pan and scraping it into the mix.  So let everything cook well and wait a little while between stirs.  It will be cooked pretty quickly, but a little bit of burning this will actually add to the flavor, just try not to go overboard. 
It is done when it looks like sloppy joe, dark red but still moist and as burnt as you like it to taste.
Put it onto your favorite rolls alone or with some lettuce and sliced tomatoes.  Toasting the rolls first makes a nice contrast in textures to the soft, sloppy filling to the sandwich.

Ingredients:
Seitan (I usually shred about 6 or 7 cutlets, not sure how that equals store-bought, but it's about 2 cups or so after shredding)
1 bottle of barbecue sauce (most brands are vegan if they are not the honey or bacon flavored varieties)
One onion
One green pepper
One clove of garlic, minced (or the jarred stuff works great)
Rolls