Season the shrimp with salt and pepper. In a 12-inch skillet over medium, heat the oil until shimmering. Add the garlic, shallots and curry leaves (if using); cook, stirring, until slightly softened and lightly browned. Add the turmeric and cook, stirring, just until fragrant and the oil takes on a yellowish hue. Increase to high and add the shrimp. Cook, stirring often, until lightly browned but not fully cooked. Add the chilies, fish sauce and ¼ cup water. Cook, stirring often, until the shrimp are lightly sauced and opaque throughout. If desired and if used, remove and discard the curry leaves and whole chilies. Season with salt and pepper.