I'm not a vegan, so let me get that out there as the first sentence. I can find recipes all over the place for veggie burgers, but all I've tried have been bland. I may indeed have an umami flavor addiction.
What are your pro tips for great taste in a veggie burger? To keep within the scope of the question, let's say that at least 75% of the weight must be made of things that would be considered vegan. Items must be available to a foodie in non-boxcar size quantiles through regular sources (though not necessarily "common" or "everyday" sources.)
I'm looking for items, not recipes.
I think I'm going to tag this question as "vegan" so 100% vegan answers are welcome too and will be up-voted.