Melt margarine or butter in a 2-quart pot over medium heat.

Add sliced onion and shredded carrots to the pot and saute until the onion is translucent.

Add diced potatoes, shredded zucchini, chicken broth, pepper, and garlic powder to the pot.

Bring the mixture to a simmer.

Reduce heat and simmer for 30 minutes, or until the potatoes are tender.

Carefully transfer the soup to a blender or food processor.

Puree the soup until smooth.

Serve the soup hot or chilled.

Garnish each serving with a dollop of sour cream, if desired.