Place lentils and water in a small saucepan and bring to a boil. Heat the oil in a medium-sized skillet. This protein-rich burger, packed with lentils, nuts, earthy mushrooms, and an exotic hint of cumin will tempt even the most committed carnivores. Transfer to a medium-sized bowl, add vinegar, and mash well. Lower the heat and simmer, partially covered, for about 30 minutes, or until the lentils are soft and the liquid is gone. The classic burger with all the fixin’s is the epitome of backyard barbecuing at its easiest and most casual.