Preheat oven to 325 degrees F. Heat the oil in a large Dutch oven or deep-sided roasting pan over medium-high heat. Season the roast with salt and pepper and brown on all sides, and then transfer to a plate. Add the garlic, leek, shallots and onion and cook until softened, about 5 minutes. Mix in the flour and tomato paste until well-combined. Slowly pour in the stock, stirring constantly, until well combined. Add the bay leaf and thyme and bring to a boil. Return the beef to the pot; cover and cook 2 hours in the oven, or until tender, turning once. Remove beef from the sauce. Slice and arrange on plates. Spoon over the sauce, sprinkle with green onions, and serve.