In a large skillet or saucepan, heat the oil with the garlic and onion over moderate heat. When they sizzle, add the cummin, coriander, giner, and red pepper flakes and saute for 1 minute. Add the tomatoes, breaking them up with your hands, and stir in the broth, lentils, and sugar. Simmer until the lentils are tender and the sauce is thick, about 30 minutes. Then stir in the yogurt and the basil and spoon over cooked pasta. Note: To make reduced chicken broth..Put the canned broth of your choice in a heavy saucepan and boil briskly until it has reduced to half of its original volume (approximately 15 minutes to reduce 2 cups of broth to one cup).