Heat the oil in a pot set over medium heat. Add the onions and garlic and cook 2-3 minutes. Add curry powder and cook, stirring, 2-3 minutes more. Stir in flour. Slowly whisk in chicken stock and coconut milk. Bring to a simmer and cook 10 minutes. Add cauliflower and cook 10 minutes more, or until tender. Stir in cilantro, season with salt and pepper, and serve.