In a medium-sized mixing bowl, whisk together coconut aminos, brown erythritol, apple cider vinegar, sesame oil, minced garlic, grated ginger, and red pepper flakes. This will be the marinade and the base for the teriyaki sauce.

Place the chicken thighs in a resealable plastic bag or a shallow dish. Pour half of the marinade over the chicken, ensuring each piece is well coated. Seal the bag (or cover the dish) and let the chicken marinate in the refrigerator for at least 30 minutes, or ideally overnight for maximum flavor.

Set the remaining half of the marinade aside—this will be used later to create a thick, keto-friendly teriyaki glaze.

When ready to cook, heat a grill or stovetop pan over medium-high heat. Add avocado oil and let it heat up.

Remove the chicken from the marinade and shake off any excess liquid. Place the chicken on the grill or pan, and cook for 5-7 minutes on one side, until nicely browned and slightly charred.

Flip the chicken using tongs and cook the other side for another 5-7 minutes, occasionally brushing with some of the reserved marinade for extra flavor. Cook until the internal temperature reaches 165°F (75°C).

While the chicken is cooking, pour the remaining marinade into a small saucepan and bring it to a gentle simmer over medium heat.

Add ½ teaspoon xanthan gum to the sauce while whisking continuously. Let it simmer for 2-3 minutes, until the sauce thickens slightly into a rich teriyaki glaze.

Once the chicken is fully cooked, remove it from the heat and let it rest for 5 minutes. This helps retain the juices.

Brush the thickened teriyaki sauce over the cooked chicken for a glossy, flavorful coating.

Garnish with sesame seeds and chopped green onions, then serve immediately.