Heat the butter in a large pot over medium high heat. Add the zucchini and onion and let them soften for about 2-3 minutes. While they soften stir in the salt, crushed red pepper and curry powder. Pour in the chicken stock and allow the mixture to simmer for 10-12 minutes. This will get the zucchini completely tender and flavorful!
When the time is up and the zucchini is completely tender, take the pot off of the heat. Stir in the Greek yogurt to make it creamy. Then use an immersion blender to make the soup completely smooth. This can also be done by transferring the hot soup (carefully!) into a blender as well.
The soup can be served hot immediately at this point in pretty bowls with crackers in it. It can also be sealed in a container and refrigerated for up to a couple of days and served cold on a hot day. Enjoy!