Preheat oven to 180°C. Pierce each sweet potato twice with the tip of a knife. Place on a baking tray.
Bake until soft, about 50 minutes. Set aside until cool enough to handle but still very warm. Reduce heat to 160°C.
Cut potatoes in half lengthways. Scoop out flesh and place in medium bowl, being careful not to tear skin. Reserve skins. Add pineapple, oil, butter, sugar, zest and salt to potato flesh. Whip with an electric mixer or whisk until slightly fluffy.
Place skin shells on baking tray. Fill with potato mixture, mounding it a little. Bake for 15 minutes. Sprinkle with pecans. Bake for a further 5 minutes.