To make the lentil filling: Add the lentils to a medium pot with the vegetable broth. Cover, and bring to a simmer and cook for 35 to 40 minutes until liquid is absorbed and lentils are soft, even mushy. Take an
immersion blender or potato masher and mash the lentils until about two thirds of the lentils are mush. This lentil mush makes everything hold together nicely.