If you’re talking about dressing up the plate with a few sprigs of cilantro, you should broaden your horizons a bit. Dressing the plate and table at a Vietnamese meal goes much further. According to Corinne Trang, author of Authentic Vietnamese Cooking (Canada, UK), garnishes are just one of the four groupings of condiments necessary to a Vietnamese meal - dipping sauces, pickles, flavorings, and garnishes.
There may be a number of dipping sauces, but the primary one is nuoc mam cham, a fermented fish sauce with lime juice, vinegar, sugar, chiles and garlic. Trang says it accompanies most dishes and is always on the table at her house.
Carrots, cucumber, daikon, and mung bean sprouts pickled in white rice vinegar, sugar, and salt are eaten more or less on a daily basis.
The flavorings Trang mentions are not served at the table, but inherent in Vietnamese cooking, such as the peanut, chile, and garlic paste known as sate.
Actual garnishes can include fried shallots, and scallion oil and fried garlic oil, which are often drizzled over soups and grilled meats or seafood. If you can’t find any of that, Trang says, there’s always cilantro, which is available everywhere.