Wieden benefits from the student crowd around the TU and the southern end of the Naschmarkt, which keeps portions generous and prices sane. It suits casual lunches and early dinners more than long formal evenings. We currently track 2 curated listings here.
If you want a broader Vienna view, start with the full restaurant directory, top 10 vegan restaurants or the vegan map.

Tiny weekday lunch spot with a daily-changing organic, seasonal vegan menu.
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