Melt the coconut oil in a soup or stock pot, then add the ground chiles and stir for 1-2 minutes until fragrant. Pour in the coconut milk and bring to boil. Add the chicken stock, galangal, lemon grass, kaffir leaves, fish sauce, and chicken and simmer for 10 minutes until the chicken is cooked through. Add the mushrooms, lime juice, coconut sugar, tomatoes and simmer for another 5 minutes until the vegetables are tender but not mushy. Serve with fresh cilantro and scallions.