Drain the tofu and crumble it by hand into small pieces resembling ground meat. Set aside.
Warm a large non-stick skillet or wok over medium-high heat.
While heating, slice the scallions thinly and separate the green parts for garnish. Dice the red onion and mince the ginger.
Add the white scallion slices, diced onion, and minced ginger to the pan and cook, stirring frequently, until softened, about 2 to 3 minutes.
Stir in the coleslaw mix and garlic, continuing to cook and stir until the cabbage is just starting to wilt, roughly 3 to 5 minutes.
Meanwhile, drain, rinse, and slice the water chestnuts if needed.
Add the crumbled tofu to the pan and stir often, cooking until most moisture evaporates and the mixture begins to stick slightly to the pan. The cabbage should remain tender with a bit of crunch.
Pour in the sriracha, tamari, and rice wine vinegar; stir everything together and cook for another 30 seconds to blend the flavors.
Remove the pan from heat and fold in the water chestnuts.
Top with the reserved green scallion slices, toasted sesame seeds, and extra sriracha to taste.
Serve right away and enjoy your protein-packed vegan stir fry!
