Meanwhile, in a large saucepan, heat 1 tablespoon of the oil. Cook the shallots over moderately high heat until lightly browned, 2 minutes; transfer to a plate. Reduce the heat to moderate. Add the remaining 2 tablespoons of oil, the garlic, curry paste, curry powder, coriander and turmeric and stir-fry for 30 seconds. Add the stock, bring to a boil and cook for 3 minutes. Add the coconut milk, fish sauce and sugar, bring to a boil and cook for 5 minutes. Add the chicken, cilantro and scallions and cook just until heated through; season with salt. Ladle the soup over the noodles and serve with the cooked shallots, lime wedges and sliced chiles.