In a large pot over medium heat, combine the oil, onion, and garlic. Sauté for 5 minutes.
Add the celery, carrot, potatoes, vegetable broth, thyme, garlic powder, and pepper. Turn the heat to high and bring to a boil, then cover and reduce the heat to medium-low. Simmer for 25 minutes or until the potatoes are fork-tender.
Stir in the coconut milk, and add salt to taste. Optionally, you can blend the soup with an immersion blender for a smoother consistency.
Garnish with sliced scallions before serving.