Heat the oil in a large saucepan over medium-high heat. Add the onion and chicken; cook until the onion softens, about 5 minutes. Add the garlic, ginger and curry; cook 1 minute longer. Stir in the potatoes and milk. Increase the heat to high and bring to a boil. Reduce the heat to medium-low.
Cover the stew and simmer 15 minutes. Stir in the peas and cook 3 minutes longer. Just before serving, season the stew with salt and stir in the cilantro.