If using bamboo skewers, soak in water for at least 30 minutes before using to prevent them from burning on the grill. We prefer metal skewers.
In a wide, shallow glass container, whisk together soy sauce or tamari, coconut sugar, garlic powder, rice vinegar, and sesame oil. Remove about 1/3 of the marinade (~2 ½ Tbsp if making the default number of servings) and reserve for making glaze.
Slice chicken thighs into ~1” chunks. Add to the container with the marinade, stir to coat well, cover, and let sit at room temperature for 30 minutes to marinate. If preparing in advance, you can marinate in the refrigerator for up to 12 hours and let sit out at room temperature for 30 minutes before grilling (this takes the chill off and prevents the chicken from burning on the outside before cooking fully).
While the chicken is marinating, whisk together the arrowroot powder and a splash of water in a small saucepan, then add the reserved marinade. Bring to a simmer, whisking frequently until thickened to a glossy glaze — about 2-3 minutes. If it thickens too much, add a little water to thin. If it’s too thin, whisk more arrowroot with water, then add to the saucepan and cook to thicken.
Once the chicken has finished marinating, lightly oil a grill pan or grill grate and preheat to medium-high. Thread cubed chicken and red onion onto skewers, alternating with 1 piece of red onion every 1-2 pieces of chicken, and ending with a piece of red onion.
Grill, turning every 3-4 minutes, until browned, beginning to char in spots, and fully cooked through (internal temperature reaches 165 F or 75 C) — about 10-15 minutes.
Transfer to a serving plate, brush the reserved glaze over the chicken, and sprinkle with sesame seeds and sliced green onion (both optional). These skewers are delicious served with rice and steamed broccoli or alongside our Creamy Sesame Noodle Salad.
Leftover grilled chicken keeps stored in the refrigerator for 2-3 days.
*Prep time includes marinating for 30 minutes. *We find chicken thighs more flavorful and moist than chicken breasts but breasts are also fine for skewers — cook time is a bit shorter, though. *Nutrition information is a rough estimate calculated with 1 tsp avocado oil and without optional ingredients. *Loosely adapted from Amanda Cooks & Styles.