In a large heatproof bowl, cover the lentils with boiling water and let stand for 15 minutes. Drain, and set aside. Meanwhile, heat the coconut oil in a large pot. Add the onions and garlic, and one tablespoon salt, a good grind of pepper, and the thyme and cumin and cook over moderate heat, stirring occasionally, until the vegetables are very tender, about 10 minutes. Add the celery and carrots and cook until they begin to soften, about 10 minutes. Add the stock, tomatoes, Worcestershire sauce and lentils to the pot. Increase the heat to high, cover and bring to a boil. Uncover, reduce the heat to moderate and simmer, stirring occasionally, until the lentils are tender, about 1 hour. Stir in the vinegar and season with salt and pepper to taste.