In a deep pan or broad-bottomed pot, heat 1 tbsp oil on med-high. Add garlic, ginger, cumin, and onion. Sauté for 1-2 minutes until fragrant.
Reduce heat to low, add tomato and coconut milk. Stir to distribute spices and onion.
Add chicken breasts. Cover and simmer for 30-40 minutes until chicken is fully cooked.
While chicken is cooking, cut potatoes in sixths or eighths depending on size of potatoes.
Heat remaining oil in a heavy bottomed pan on high. Add potatoes so that they are in a single layer, not over-lapping. Cook for 3-5 minutes per side, turning when browned. When all sides are browned, remove from heat and set aside.
Uncover and add potatoes for a remaining 10-15 minutes until chicken is very tender and some of liquid is reduced.
Add rice vinegar and salt.
*To peel the tomatoes easily, blanche them:
Remove the core of the tomatoes (without cutting it in half). On the other side of the tomato, make a shallow X-cut in the skin.
Place the tomatoes in a bowl and completely cover with boiling water. Leave for 15 seconds, dump the hot water out and plunge the tomatoes into ice water. Leave until cool enough to handle.
The edges of the skin at the X should have started pulling away from the tomato flesh, making them easy to grasp and peel away.