Yes you can freeze red lentils. Prepare dal and you can divide it in small portions in small freezer freiednly boxes and freeze. Stays good to use for about a month. Thaw Dal in refrigerator few hrs before serving. Reheat in microwave or on stove top in pan. You can add onion garlic masala befroe freezing or, only boil dal, cool completely, freeze it and add tempering just before serving.