There was a groupon for Flavor Spot (the Waffle Cart) yesterday but due to server failures it's been extended through midnight of today. Flavor Spot does have one dedicated vegan item and a couple others that can be made so (but if you want a vegan "nutella" try Freddie Guys Hazelnut booth at the Saturday Farmers Market). The Flavour Spot owner said a while ago that only 1% of sales are vegan which seems low for PDX.
If you haven't already then you can access the Flavour Spot offer through the Main Groupon Page
then click at the top of the page where it says, "Good news: If you were unable to buy yesterday's deal for Flavour Spot, you've got an extra day to purchase your Groupon."
The offer is good for the cart locations downtown and Fremont/Mississippi.