In a small pot, bring the rice vinegar, white vinegar, white sugar, and salt to a boil over high heat. With a julienne peeler, peel the carrot and daikon and place in a medium heat-safe bowl. When the pickling mixture has come to a boil, pour over the vegetables. Refrigerate. Please note, this can be made ahead of time.
Thoroughly mix the vegan mayonnaise and sriracha.
Press the tofu block, squeezing as much moisture out as possible. Slice the block in half, then slice lengthwise to create four equal pieces – about 4 oz. each.
Place the cornstarch in a shallow bowl and season with salt and pepper. Press the tofu blocks on all sides in the cornstarch and shake off any excess.
Heat the oil in a medium nonstick skillet and sear the tofu pieces on each side until browned.
To build the sandwich, lightly spread 1 Tbsp. of vegan sriracha mayonnaise on the tops and bottoms of the burger buns. Place seared tofu piece on bottom bun, ⅓ – ½ cup of the pickled root vegetables on top, and finish with 4 slices of cucumber and the cilantro leaves.