Restricting Solitary Confinement in Immigration Detention Act of 2019 This bill places limits on solitary confinement in U.S. Immigration and Customs Enforcement (ICE) facilities. Solitary confinement shall be (1) limited to the shortest duration and least restrictive conditions necessary, and (2) consistent with the rationale for placing the alien in solitary confinement. Administrative segregation (a type of solitary confinement) shall (1) be limited to where a substantial and immediate threat makes such segregation necessary; (2) be limited in duration, with certain exceptions; and (3) not be used to discipline. An alien who requires protection (1) may be placed in solitary confinement upon the alien's request, and (2) shall be transferred to a safer alternative upon the alien's request. The bill places additional restrictions on placing a vulnerable individual in solitary confinement, such as an individual who (1) is a minor; (2) has a serious disability or mental illness or; or (3) is pregnant or had just given birth. Generally, such individuals may not be placed in solitary confinement absent a substantial and immediate threat. An alien may not be placed in solitary confinement based on (1) identification as lesbian, gay, bisexual, or transgender; (2) HIV status; (3) race, religion, or nationality; or (4) the alien's report of misconduct. An alien in solitary confinement shall receive a weekly mental health evaluation. The Office for Civil Rights and Civil Liberties within the Department of Homeland Security shall have unrestricted access to ICE facilities, records, and personnel. The bill imposes various training, reporting, and data collection requirements related to solitary confinement.