Heat the oil in a large skillet or sauté pan over medium heat. Add the kielbasa and cook for about 3 minutes, until lightly browned. Add the onion, bell pepper, and garlic and cook, stirring occasionally, for 4 to 5 minutes, until the vegetables have softened. Push the vegetables and kielbasa to the perimeter, making a well in the center of the pan. Add the chicken and sauté until lightly browned but not cooked through, about 3 minutes. Stir in the rice, stock, tomatoes, tomato paste, cayenne, and bay leaves. Turn the heat to low, cover, and simmer for 17 minutes, until nearly all of the liquid has been absorbed by the rice. Uncover, add the shrimp, and cook for 2 to 3 minutes, until the rice is tender and the shrimp is cooked through. Discard the bay leaves. Season with salt, black pepper, and hot sauce and garnish with the scallions, if using.