Heat the olive oil in a large cast iron skillet or Dutch oven over medium heat. Add the sausages and brown on all sides, about 7 to 8 minutes. Remove from skillet and reserve.
Add onions and peppers to the skillet and saute until tender and golden brown, about 6 minutes. Add the garlic and saute until fragrant. Stir in the tomato paste, beer, and BBQ sauce. Cook for a few minutes, then add the sausages back to the pan. Reduce the heat and simmer until the sauce is nice and thick, about 10 minutes.
Slice the bread open, put on sheet tray, and toast in the oven while the sausage is simmering. Remove the bread from the oven and fill with the sausages and peppers.