This vegan version of the classic shepherd's pie is made with lentils instead of meat, making it a hearty and nutritious meal that is perfect for vegetarians. The lentils are cooked with onions, carrots, and celery in a rich tomato sauce, and then topped with a layer of creamy mashed potatoes. The dish is then baked until golden and bubbly, creating a comforting and satisfying meal that is perfect for a cozy night in.