Wash and dry produce. Halve, peel, and very thinly slice onion. In a small bowl, combine half the vinegar (you’ll use the rest later), 1/2 tsp sugar (1 tsp for 4 servings), and a pinch of salt and pepper. Add 1/4 of the sliced onion; toss to coat. Set aside, stirring occasionally, until ready to serve.

In a medium bowl, combine sour cream, remaining vinegar, 1/2 tsp sugar (1 tsp for 4 servings), and sriracha (start with half and add more if you like things spicy). Stir in half the cabbage. Season with salt and pepper. Set aside, stirring occasionally, until ready to serve.

Heat a large drizzle of oil in a large pan over medium-high heat. Add remaining onion and cabbage and season with salt and pepper. Cook, stirring, until slightly softened, 2-3 minutes.

Meanwhile, pat chicken dry with paper towels. Add to pan with veggies along with another drizzle of oil, salt, and pepper. Cook, stirring often, until chicken is browned and cooked through, 4-6 minutes.

Add teriyaki sauce to pan; bring to a boil. Reduce to a low simmer and cook until sauce is slightly thickened and coats chicken and veggies, 4-6 minutes. Stir in half the sesame seeds. Season with salt and pepper.

Wrap tortillas in damp paper towels and microwave until warm and pliable, 30 seconds. Divide chicken and veggie mixture (using a slotted spoon if needed) between tortillas. Top with cabbage slaw and pickled onion. Sprinkle with remaining sesame seeds and serve.