Mexican food in Japan can be a surreal and bizarre experience. This will be either totally awesome or incredibly awkward. Either way I want to eat there badly.
Further googling in-depth research yields us a Japanese foodie web site called ｢Food Event Hunt｣ (translated page here) that covered the ｢フィエスタ メヒカーナ｣, aka ｢Fiesta Mexican｣ where our new favorite taco truck made an appearance.
Best line: このブリー ト、かなりボリュームありました。 (“This burrito had considerable volume.”).
And through some judicious internet translating and stalking, we have discovered the home base of our now world-famous Aguacate Taco Truck. On your next visit to Tokyo, approach slowly and make no sudden movements.