A permanent resident (called lawful permanent resident or LPR) or conditional resident (CR) who has remained outside the United States for longer than one year, or beyond the validity period of a Re-entry Permit, will require a new immigrant visa to enter the United States and resume permanent residence.  You can learn more about Returning Resident Visas on usvisas.state.gov.

The Embassy in Port Louis, Mauritius, does not process immigrant visas. Immigrant visas are processed at the U.S. Consulate General in Johannesburg, South Africa.