Meanwhile, Make the Gravy
In a medium cast-iron skillet, heat the oil. Add the andouille and cook over moderate heat, stirring, until the fat is rendered and the sausage is crispy, 8 minutes. Add the onion and cook, stirring, until translucent, 3 minutes. Stir in the green pepper and garlic and cook, stirring, until the garlic is fragrant, 2 minutes. Sprinkle in the flour and stir until incorporated; add the tomato and cook over moderately low heat, stirring, until it starts to break down, 3 minutes. Add the stock and bring to a simmer; cook until the gravy is thick enough to coat the back of a spoon, 5 minutes. Stir in the scallions and season with salt.