Heat the olive oil in a large soup pot over medium heat until shimmering. Add the minced garlic and cook, stirring frequently, until fragrant and just beginning to turn golden, about 1 minute.
Add the chopped carrots, parsnips, and diced sweet potato to the pot. Stir well to coat the vegetables with the fragrant garlic oil, and cook for about 5-7 minutes until they start to soften and turn slightly golden.
Sprinkle the ground cumin over the vegetables and stir to evenly distribute the spice, enhancing their earthy aroma. Cook for another minute to toast the cumin slightly.
Pour in the vegetable broth, bringing the mixture to a gentle boil. Reduce the heat to low, cover the pot, and let the soup simmer for about 25-30 minutes until the root vegetables are tender when pierced with a fork.
While the soup simmers, prepare the greens by chopping the kale into bite-sized pieces. This can be done quickly in a food processor or with a sharp knife.
Once the vegetables are tender, use an immersion blender or transfer the soup carefully to a blender to puree until smooth and creamy, about 2-3 minutes. Be cautious of the hot liquid—blend in batches if necessary.
Return the pureed soup to the pot if using a standalone blender. Stir in the chopped kale and cook uncovered over low heat for 5-7 minutes until the greens are wilted and tender, adding a splash of water if it gets too thick.
Add the citrus zest to brighten the flavors, stirring well to distribute. Season with salt and freshly ground black pepper to taste, adjusting the seasoning as needed.
Remove the soup from heat and ladle into bowls. Optionally, garnish with extra citrus zest or a drizzle of olive oil for added brightness and richness.