Heat the avocado oil in a medium-sized pot set over medium-high heat. Add the onion; saute, stirring for 2 to 3 minutes
Stir in the cumin; cook for about 2 minutes to bring out the pungent aroma of the spice.
Stir in the carrots, stock or broth and salt, if using; simmer partially covered, for 30 to 40 minutes or until the carrots are tender. Remove from the heat and let cool.
Transfer the soup to a blender or food processor, fitted with a metal blade, and process until smooth.
Blend in the orange juice and lime juice, if using. Transfer to a bowl or storage container, cover and refrigerate until well chilled.
Serve cold in chilled soup bowls. Garnish with orange zest and dill, if desired.