To make the pickled vegetables, place them in a bowl or jar and add rice vinegar. Toss several times to coat, and set aside.
Slice the tempeh and place in a shallow dish. Whisk together the marinade ingredients (soy sauce, maple syrup, lime juice, garlic, ginger, and red pepper). Pour over the tempeh. Set aside for 15 minutes, stirring after a few minutes to make sure all pieces are covered and soaking up the flavors.
Preheat a large non-stick pan over medium heat. Add cooking oil to the pan if desired. Arrange the tempeh in the pan, reserving excess marinade and bits of garlic in the bowl. Cook tempeh for 3 to 4 minutes per side or until golden. Pour the reserved marinade into the pan. Cook for about 1 minute, carefully stirring so the garlic doesn't burn. Remove from heat.
Stir together the vegan mayonnaise and sriracha, if using. Spread mayo on both pieces of bread. Add tempeh, pickled veggies, and cilantro. Serve with extra mayo and more pickled vegetables on the side.
Tips for selecting breadAn authentic Vietnamese-style baguette won't be easy to find for most of us. Long French baguette can be cut into shape. Or use hoagie rolls. Look for bread with an exterior crust since the crunch is a large part of the banh mi experience. However bread that is too tough will be difficult to eat. Ciabatta bread is another option. For homemade try this Vietnamese baguette recipe.Nutrition will vary depending on exact ingredients used. Store leftover pickled vegetables in the refrigerator for up to a week. The cooked tempeh keeps for up to 5 days.