Salty tamari-spiked tempeh, slightly bitter spinach, and toasted sesame oil perform a lovely flavor dance and make a fine last minute dinner.
Keep a package of tempeh in the freezer. It will be there when you decide at the last minute to make this for dinner. Simply "plump" the tempeh in tamari water 5 minutes longer than with unfrozen tempeh.
I use Westsoy brand Five Grain Tempeh, and it seems to be easily available, but there are more tempeh choices out there. Any tempeh is fine for this recipe.