Combine the lentils and the water in a large saucepan. Heat to boiling. Reduce the heat to very low and simmer covered until tender but still firm to the bite, about 25 minutes for green lentils or 10 to 40 minutes for brown lentils depending on their age.
Heat the butter or fat in a large sauté pan over low heat. Add the vegetables and pancetta and cook, stirring occasionally, until te