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.
4 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.
Twice-Baked Stuffed Sweet Potatoes can be made up to a day ahead. Bake and stuff the potatoes as directed. Place in a shallow dish, cover loosely and refrigerate. Remove from the refrigerator 30 minutes before baking as directed in the recipe.