Heat 1 tablespoon of oil over medium-high heat in a large frying pan. Brown the chicken on all sides.
If needed, add the rest of the oil to the pan. Quickly saute the onions and garlic together with the chicken for about a minute just to soften and release the flavors.
Lower the heat and add the honey, dark & light soy sauce, rice wine vinegar, and black pepper. Mix until combined. Slowly add the water and stir to combine. Mix in the brown sugar stirring until dissolved. bring the mixture to a boil to thicken.
Pour the mixture into the slow cooker, cover and cook on low for 4-6 hours, or until the chicken is cooked through and tender.
Serve over rice.
The sauce came out quite thick when I added it to the slow cooker and I worried it would burn. But my slow cooker builds up a lot of condensation that drips into the food as it cooks, thinning the sauce. If your slow cooker doesn’t do that, I would suggest saving the thickening until the end so it doesn’t burn around the sides.