Heat the oil in a 5-qt nonstick Dutch Oven and saute the onions and garlic over low heat, stirring constanly for 5 minutes, or until the onions are soft and begin to brown. Stir in the lentils and add the chicken stock. Bring to a boil, lower the heat, cover and simmer for 15 to 20 minutes. Then stir in the tomatoes, tomato paste, hot pepper flakes, cumin, allspice, coriander, salt and pepper. Simmer for 10 to 15 minutes more, or until the lentils are soft but hold their shape.