In a medium bowl, mix the garlic, ginger, apple juice, brown sugar, ketchup, cider vinegar and soy sauce together.

Place the chicken thighs into the crockpot. Pour the mixed sauce into the crockpot and over the chicken, then use tongs to coat the chicken thighs in the sauce.

Cook on high for 4 hours, until the chicken is tender.

Sprinkle with red pepper flakes and chopped green onion on top. Serve with steamed rice.

To slightly thicken the sauce once the chicken has finished cooking, remove about a cup of the sauce from the crockpot and mix it in a small saucepan with 1 tablespoon of cornstarch. Let it come to a boil so that the cornstarch will dissolve and thicken, then stir it back into the crockpot with the rest of the sauce and the chicken.