Heat medium-large saute pan with 1 tablespoon of the vegetable oil and saute the onion for 3-4 minutes or until limp. Pour in the coconut milk then bring to a boil, stirring. Stir in the curry paste, curry powder, fish sauce and sugar. Allow to simmer for about 8 minutes to blend and concentrate the flavors.
Add the potatoes to the curry mixture, cover and continue to simmer gently for about 20 minutes.
Meanwhile, place a large saute pan over medium-high heat and add the remaining tablespoon of vegetable oil and the tablespoon of sesame oil. Saute the chicken chunks until golden brown (they do not have to be cooked through). Add the browned sautéed chicken to the curry mixture, cover and cook over low heat for another 10-15 minutes, until the chicken is cooked through and the potatoes are tender.
Before serving, stir in the lime juice, cilantro, and basil. Serve immediately, sprinkled with the lime zest.