Prepare Chicken: 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 tsp salt and 3/4 tsp 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. (For oven instructions, see Note 1.)
Sweet Potatoes: Preheat oven to 425°F. Toss sweet potatoes with olive oil, seasonings, and salt and pepper (about 3/4 tsp salt, 1/4 tsp pepper). Spread on a sheet pan in a single layer. Bake for 27–35 minutes, flipping every 10–15 minutes, until charred and tender.
Slaw: Whisk mayo, mustard, vinegar, and honey in a large bowl. Season with salt and pepper (about 1/2 tsp salt, 1/4 tsp pepper). Add cabbage and carrots; toss with tongs to coat. Chill until ready to serve.
Sauce: Combine all sauce ingredients in a small bowl. Adjust salt and pepper to taste (about 1/4 tsp each). Whisk until smooth, then refrigerate to let flavors meld.
Assembly: 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.
Notes
Note 1: For oven-baked chicken:
Preheat oven to 425°F and line a baking sheet with foil.
Prepare and season chicken as above.
Lay chicken thighs flat on the prepared sheet pan, spaced out, and bake for 15 minutes.
Move the oven rack to 8 inches from the heat source, switch to broil, and broil chicken for 7–10 minutes until nicely blackened and caramelized.