I can't claim that these sandwiches are authentic, but I can tell you for sure that they're delicious -- and that I already want another one. If I'd had the space and wherewithal to title them really good banh mi-ish sandwiches with really good char siu-ish tofu, that would've been the perfect title.
For the pickled vegetables:
Place the cut vegetables into a shallow bowl. Pour the 1/2 cup vinegar overtop and stir to coat. Let sit until ready to assemble sandwiches, stirring occasionally. Before using, drain off excess vinegar.
For the char siu tofu:
In a 9x13-inch baking dish, whisk together the garlic, five spice powder, brown sugar, soy sauce, hoisin sauce, 1 tablespoon of the oil and the 1 tablespoon of vinegar. Dry the tofu slices as well as possible by pressing lightly with your hands between thick layers of paper towels. Add tofu slices to baking dish in a single layer and turn to coat top and bottom of all slices completely with marinade. Let sit for 10 minutes.
In a 10- or 12-inch nonstick skillet, heat one tablespoon of the oil over medium-high. Add half the tofu slices in a single layer and cook undisturbed until beginning to char on the underside, then flip and do the same for the other side. Remove to a plate and repeat with remaining tablespoon of oil and tofu slices. When tofu is cooked, pour any remaining marinade into pan and cook, stirring, for less than a minute, until thickened slightly. Pour over tofu slices.
For the sandwiches:
Lightly toast the rolls, then split each one lengthwise down the middle, leaving the bottom intact so the roll can open like a book. Spread a generous schemer of mayo onto each of the inside faces. Tuck in three slices of tofu and a generous serving of pickled vegetables. Drizzle with sriracha and top with plenty of cilantro leaves and jalapeño slices to taste. Serve immediately.