Heat oil over medium-high heat in a large stock pot. Add leeks and shallots and season with salt and freshly ground black pepper. Cook until soft and translucent then add celery and cook a couple minutes more. Add garlic, cook another minute more then add squash and season again with salt and pepper. Cook until squash is just beginning to soften, about 3-4 minutes.

Add remaining ingredients and bring to a boil. Reduce heat, cover and simmer over low heat until lentils are soft, about 30-40 minutes. Taste and adjust seasoning, you also might need to add more stock if soup seems too thick.

While soup is cooking combine all salsa ingredients in a medium bowl. Add a little freshly ground black pepper and add salt if necessary (this will depend on the saltiness of the capers and your tastes).

To serve, ladle soup into bowls and top with a dollop of salsa verde.