Saint Lucia citizens - Ordinary passport holders are required to have visa to enter Turkey. They can obtain three month multiple entry visas at the Turkish borders gates. Official passport holders are exempted from visa for their travels up to 90 days.
Turkey has an online Turkish Visa Application System where you can apply for e-Visa online and pay your fees in a few minutes. Saint Lucia citizens who meets the required criteria can obtain a visa on arrival or online at Turkish Visa Application System - https://www.evisa.gov.tr/en/apply/.