how long to cook red lentils
1 Be sure to use a large enough saucepan as the lentils will double or triple in size. 2  Bring to a boil, cover tightly, reduce heat and simmer until they are tender. 3  For whole lentils, cook time is typically 15-20 minutes. 4  For split red lentils, cook time is typically only about 5-7 minutes. For whole lentils, cook time is typically 15-20 minutes. 2  For split red lentils, cook time is typically only about 5-7 minutes. 3  Be sure to season with salt after cooking â if salt is added before, the lentils will become tough.