Heat 1 tbsp. of the oil in a large, deep skillet with a tight fitting lid over medium heat. Once it's hot, add the sausage and cook until browned. Then remove them to a seperate plate and set it aside. Add the additional oil and the onion, peppers and celery with a big pinch of salt. Cook, stirring often, until softened, about 7-9 minutes. Stir in the garlic and cook that until fragrant.