Bring lentils and two quarts of water to a boil, reduce heat and simmer 20-30 minutes or until tender. Drain the lentils thoroughly and set aside to cool. Clean mushrooms and then finely chop the stems and caps. Heat one tablespoon oil in skillet and add onions. Cook until softened, about five minutes. Add the garlic, mushrooms and cumin and cook for five minutes more. Season with salt and pepper to taste and remove from heat. Break up the bread and put pieces into food processor bowl or blender; process into crumbs. Place two cups of the crumbs into large bowl, reserve remaining crumbs. Add lentils to processor and pulse until somewhat pasty. Transfer lentils to bowl with crumbs, stir in mushroom mixture and mix well, using clean hands. If mixture is too wet to shape into patties add some of the reserved breadcrumbs. Chill the mixture at least one hour and up to two days. Form the burger mixture into four patties. Heat the remaining tablespoon oil in a large skillet, preferably cast iron, over medium heat. Fry the patties until golden brown, about three minutes. Flip and cook about three minutes on the second side.