In a Dutch oven or stock pot, heat oil over medium heat. Add onion; cook and stir until tender,4-5 minutes. Add garlic and ginger; cook 1 minute longer. Stir in carrots, broth, zest, salt and pepper; bring to a boil. Reduce heat; simmer, covered, until carrots are tender, 10-12 minutes. Pulse mixture in a blender or with an immersion blender until desired consistency; stir in lemon juice. If desired, garnish with additional lemon zest.
Freeze option: Cool soup; freeze in freezer containers. To use, partially thaw in refrigerator overnight. Heat through in a large saucepan over medium-low heat, stirring occasionally and adding a little broth or water if necessary.