Place the chicken in the bottom of the crockpot.
Mix soy sauce, sugar, pepper, garlic, red pepper flakes and olive oil in a small bowl. Pour over chicken.
Place onion slices on top of chicken.
Cover with lid and cook on high for 2 hours then on low for 3-4 hours or until ready to serve. (Cooking times will vary depending on crockpot and whether chicken is fresh or frozen.)
Serve chicken over rice and garnish with fresh parsley.