Fire up your smoker for cooking at 225 F. You can also cook the sausages on a gas or charcoal grill.
Add the sausages and smoke for 2 hours or until the internal temperature is 155 F.
Toast the buns, if desired.
Assemble the sandwiches by adding the sausages to the buns and loading up on the topping. Add a bit of spicy mustard too, if desired.
For the topping
Note: I prefer to make this topping on a griddle insert on my grill since I'm already outside smoking the sausage. You can also make it in a large skillet on your stovetop.
Heat a large skillet over high heat.
Add onions and peppers and saute until tender and golden brown, about 6 minutes.
Add the garlic and saute for 3 minutes.
Stir in the tomato paste, beer, and BBQ sauce.
Cook for 5 minutes then reduce the heat to a simmer and cook another 10 minutes, stirring occasionally. The sauce should be nice and thick. If it gets too thick add a bit more beer or some water.