In a large pot, sauté onion, garlic, ginger, curry powder and red pepper flakes with a pinch of salt in about a tablespoon of olive oil over medium heat until the onions are softened and translucent.
Add about 2-3 ladlefuls of hot broth from the soup to the butter/flour mixture, and whisk until completely smooth. Pour the mixture back into the pot with the soup.
Bring the soup back up to a bubble, then add the coconut milk and spinach and stir to incorporate. Cook until the soup is completely heated through and the spinach is just wilted.