Heat a wok or skillet over medium-high heat. Add the oil and heat until hot for 30 seconds. Add the pepper flakes, lemon zest, garlic, and curry powder and stir-fry until fragrant, about 15 seconds. Add the coconut milk, soy sauce, sugar, and salt and cook, stirring occasionally, until the sauce thickens slightly, about 1 1/2 minutes. Add the basil. Pour into a bowl.