Preheat your oven to 350°F (175°C).

In a large skillet over medium heat, cook the sliced kielbasa until it starts to brown, about 5-7 minutes. Remove the kielbasa and set aside, leaving any rendered fat in the skillet.

In the same skillet, add the diced onion (and bell pepper if using). Sauté until the vegetables are softened and slightly browned, about 5 minutes. Add the minced garlic and cook for another minute until fragrant.

In a large mixing bowl, combine the canned baked beans (with their sauce), brown sugar, mustard, ketchup, apple cider vinegar, Worcestershire sauce, salt, pepper, and smoked paprika if using. Add the cooked kielbasa and sautéed vegetables to the bowl and mix well.

Transfer the mixture to a greased 9x13 inch baking dish. Cover with aluminum foil and bake in the preheated oven for 45 minutes.

After 45 minutes, remove the foil and continue baking for another 15 minutes, or until the top is bubbly and slightly caramelized.

Let the baked beans rest for a few minutes before serving. This dish can be served hot as a main course or side dish.