Trim excess fat from chicken thighs and pat dry. Combine chicken, olive oil, and balsamic vinegar in a bowl; toss with tongs to coat. Sprinkle seasonings over chicken and add salt and pepper (about 1 teaspoon salt and ¾ teaspoon pepper). Toss again until evenly coated. Place flat, smooth-side down in Air Fryer. Air fry at 400°F for 10–12 minutes, flipping halfway, until the internal temperature reaches 160°F. Rest chicken for 5 minutes, then thinly slice.

Preheat oven to 425°F. Toss sweet potatoes with olive oil, seasonings, and salt and pepper (about ¾ teaspoon salt, ¼ teaspoon pepper). Spread on a sheet pan in a single layer. Bake for 27–35 minutes, flipping every 10–15 minutes, until charred and tender.

Whisk mayo, mustard, vinegar, and honey in a large bowl. Season with salt and pepper (about ½ teaspoon salt, ¼ teaspoon pepper). Add cabbage and carrots; toss with tongs to coat. Chill until ready to serve.

Combine all sauce ingredients in a small bowl. Adjust salt and pepper to taste (about ¼ teaspoon each). Whisk until smooth, then refrigerate to let flavors meld.

Divide cooked quinoa among 4 bowls. Add chicken, sweet potatoes, and slaw. Top with fried onions (if using) by crushing with your hands over the bowls. Drizzle with sauce just before serving.