This creamy soup is a riff off callaloo, a traditional West Indian soup that is made with the leaves of the callaloo plant. Because that plant is not native in the United States, the soup is often made here with spinach or even collard greens -- but with the abundance of zucchini, this version, served hot or cold, offers a new twist that still employs many of the same flavors!
Heat the vegetable oil in a large pot over medium-high heat. Add the onions and a pinch each of salt and pepper. Cook until the onions start to color, stirring occasionally, about 3 minutes. If the pot is dry, add a bit more oil. Add the zucchini and bay leaf and season with salt; cook, stirring until coated, about 2 minutes. Add the garlic, ginger, nutmeg and 1 teaspoon of the curry powder; cook, stirring, for 30 seconds. Add the vegetable broth and coconut milk. Cover and bring to a boil.
Reduce the heat and simmer for 15 minutes. Remove from the heat, then remove and discard the bay leaf. Stir in the remaining 1/2 teaspoon curry powder, if needed. (If serving chilled, let cool to room temperature.) Working in 2 batches, transfer the soup to a blender; pulse, then blend on low speed, gradually increasing the speed to high, until smooth. Add salt and pepper to taste. (For the cold version, refrigerate until completely chilled, at least 2 hours.)
When ready to serve, divide the zucchini noodles between each bowl, then stir the lime juice and cilantro into the soup and pour over the zucchini noodles in each bowl. Garnish with cilantro sprigs. Serve with lime wedges and Sriracha.