Brown the kielbasa. Heat a drizzle of olive oil in a large skillet over medium heat. Add the sliced kielbasa and sauté until deeply golden and crispy around the edges. This adds texture to the sausage and builds flavor in the skillet for the sauce. Transfer to a plate.
Cook the onion. Add a little more olive oil to the skillet if needed. Add the chopped onion and sauté for about 5 minutes, until softened.
Add the bell pepper. Stir in the bell pepper and garlic cook for another 3–5 minutes, until beginning to soften.
Make the barbecue sauce. Add the barbecue sauce, brown sugar, water, red pepper flakes, and black pepper. Stir to combine.
Simmer. Return the kielbasa to the skillet. Bring the sauce to a gentle simmer and cook for 2–3 minutes, stirring until the sauce thickens slightly and coats the sausage and vegetables.
Serve. Serve warm over rice or pasta, or alongside crusty sourdough bread.
