Heat pan, and add 1 tbsp oil.
Brown/sear chicken on both sides, then remove from pan.
Don't worry that the chicken is not fully cooked, we will return to pan again.
Add the other 1 tbsp oil, and saute onion & garlic until fragrant.
Then add chicken back in the pan.
Add dark soy, sugar, water, and fish sauce.
Cook until sugar is melted, chicken cooked, and sauce reduced.
Remove from heat and stir in lime juice.