Dice 3 of the onions. Heat a large, heavy skillet and add 2 tablespoons of the olive oil and the diced onions. Cook, stirring frequently, for 10 to 15 minutes until browned and caramelized. Remove to a bowl or plate and set aside.
Combine the lentils and water in a large covered pot. Bring to a boil, then reduce the heat to low and simmer for 15 minutes.
Add the cooked onion to the lentils, along with the rice and salt. Cover and simmer for 20 minutes, until the rice and lentils are soft. Remove from heat and let stand for 5 minutes.
While cooking rice and lentils, slice the remaining 2 onions thinly into rings. Heat the skillet again and sauté them in the remaining oil.
To serve, top the lentils with the sautéed onion rings.
This is a flavorful dish and very good served hot or cold.