In a large, deep skillet, heat the oil until shimmering. Whisk in the flour and cook over moderately high heat, whisking constantly, until lightly browned, about 2 minutes. Add the onion, bell pepper, celery, and garlic. Season the vegetables with salt and black pepper and cook over moderate heat, stirring, until softened, about 6 minutes. Add the sausage and tomato paste and cook for 2 minutes. Add the broth and simmer until thickened, 3 to 4 minutes. Stir in the chicken and simmer until cooked through, 5 minutes. Season with salt and black pepper and serve over rice, with hot sauce.