Bring the water and bouillon cubes to a boil.

Rinse the lentils well and add them to the pot. Cover and simmer over low heat until the lentils are cooked, about 1 hour.

Add the oats and cook, stirring occasionally to prevent sticking.

Add the vermicelli noodles and let the soup boil for about 10 minutes.

You can add the cooked beef with sautéed onions either at the beginning of cooking or at this stage.

Pour into a serving bowl and enjoy.