Heat 3 tablespoons oil in a large skillet over medium-low heat. Add onion; cover and cook 15 minutes or until soft, stirring occasionally. Uncover and increase heat to medium; cook 25 minutes or until golden brown, stirring occasionally. Keep warm.
While onion cooks, bring 4 1/2 cups water to a boil in a large saucepan. Add lentils; cook 20 minutes or until tender. Stir in 1/2 cup caramelized onion, rice, salt, and pepper. Cover, and cook 25 minutes or until lentils and rice are tender. Spoon lentil mixture into a shallow dish; top with remaining onion. Drizzle 1 tablespoon oil over lentils.