Heat olive oil in a medium skillet over medium-high heat.

Add carrots, garlic, and onion to the skillet.

Cook, stirring frequently, for 3 minutes or until onion is translucent.

Add cumin, coriander, and turmeric to the skillet.

Cook, stirring constantly, for 1 minute.

Scrape mixture into the slow cooker.

Add lentils to the slow cooker.

Stir in stock and orange zest.

Cook on low for 7 to 9 hours or on high for 3 to 5 hours or until lentils are very soft.

Remove 2 cups of solids from the soup with a slotted spoon.

Puree the removed solids until smooth in a food processor fitted with a steel blade or in a blender.

Return the puree to the soup.

Season the soup with salt and pepper to taste.