In a large, heavy pot, cook the onions and garlic in about 3 tablespoons of oil, over moderate heat, stirring, until the onions are softened and translucent, about 3-5 minutes. Increase heat to medium high and add pork. Season well with salt and pepper. Sauté until lightly browned. Using a slotted spoon, scoop out pork and onions and set aside. Set cooking pan with drippings aside to use for making the sauce.