How to Make It
Preheat the oven to 375°. In a large saucepan, bring the red lentils, rice, sliced onion, chicken stock, water, cumin and allspice to a boil. Add a generous pinch of salt, cover and simmer over moderately low heat, stirring, until the lentils and rice are tender, about 20 minutes.
In a blender, puree the soup in batches until very smooth. Return the soup to the saucepan and season with salt. Add more water for a thinner consistency, if desired.
Meanwhile, in a large skillet, heat the oil until shimmering. Add the chopped onions and a generous pinch of salt and cook over moderate heat, stirring occasionally, until golden, 15 minutes. Remove from the heat.
Spread the bread on a rimmed baking sheet. Bake for 10 minutes, until nearly crisp; let cool slightly. Reheat the soup, if necessary. Ladle the soup into shallow bowls, top with the fried onions and croutons and serve.