In a large stockpot, saute the onion in olive oil over medium-low heat, until softened - about eight minutes.
Stir in lentils, rice, carrots (if using), cumin, turmeric, salt, and pepper.
Add your broth, and then bring to a boil. Once boiling, turn the heat to low and allow to simmer for 45-50 minutes (rice should be soft and lentils fully cooked). Turn off the heat and add your preserved lemon.
Using an immersion blender, or a high-powered blender (like a Vitamix) pulse a few times to achieve your desired consistency (I like mine with a bit of texture still rather than pureed).
Garnish with green onion and herbs if desired, and serve.