If the Belgian passport holders want to apply visa at Vietnam Embassy, they should to know that:
Visa administrative Institution: Vietnam Embassy
Processing time: depends on you how fast you need. But for sure, you should make a call to Vietnam Embassy for details.
Required Documents: passport, money and 1 new envelope with stamp on it and your exact home address in order to avoid losing issues.
How to apply: please take a look at contact information of Vietnam Embassy below
VIETNAMESE EMBASSY IN BRUSSELS, BELGIUM
Address: 01 Boulevard Gesnesneeral Jacques, 1050 Bruxelles
Phone: (322) 379 2737
Fax: (322) 374 9376