Preheat oven to 350 degrees F. Line a baking sheet with parchment paper.
Combine sliced apples, sweetpotatoes, walnuts, dates, brown sugar, lemon juice, cinnamon and salt in a large bowl. Toss until well mixed.
On a clean work surface, unroll phyllo sheets. Lay out 1 sheet on the prepared pan. Brush lightly with some of the oil. Repeat with the remaining 5 sheets, stacking them and brushing each with oil.
Using a slotted spoon, spoon the sweetpotato mixture in a strip along a long side, leaving a 2-inch border. Fold in the short sides and roll up into a log. Place seam-side down on the prepared pan. Brush with the remaining oil. Bake until pastry is golden brown, about 30 minutes.
Use a fine-mesh sieve lightly dust the pastry with confectioners’ sugar. Serve warm.