Cook lentils in 4 cups of water as per package instructions (bring to a boil and simmer for 15-20 minutes until the lentils are tender). Take care not to make them mushy. Drain the excess water and set the lentils aside to cool slightly.
Make the dressing: Whisk all the ingredients for dressing in a small bowl.
Pour dressing on the lentils along with walnuts and cranberries. Mix well and refrigerate until ready to serve.