There is NO embassy of Vietnam in Mauritius, therefore, Mauritian passport holders may go to the location of the embassy of Vietnam in countries close to Mauritius such as Mozambique, Tanzania or South Africa, to apply for a visa.
Visa On Arrival (VOA) is one of the several visa types issued by the Vietnamese Immigration Department to foreigners intending to enter the country.
If you want to pick up your visa on arrival at international airports of Vietnam, you should apply online through a website for Vietnam visa or contact your travel agent in Vietnam to ask for a visa approval letter from Vietnam Immigration Department.
Then upon arrival at the international airports of Vietnam, you are required to show the visa approval letter to get visa stamped on your passport.