How do you prepare lentil soup?

There are many ways to prepare lentil soup.  However a common method involves cooking onions, celery, and carrots in olive oil for several minutes.  Then you would add aromatics, such as garlic and spices, and cook for a minute.  Then you would add lentils and broth (or water) and bring to a simmer.  The soup should simmer for at least 30 minutes until the lentils are fully cooked.  Once finished cooking, you would garnish the soup with croutons, herbs, or drizzle with oil.