In a bowl, mix the lukewarm water, oil, lemon juice, and salt. Then stir in half of the flour for about 1 minute. After that, add the rest of the flour and mix until a shaggy dough forms.

Turn the dough onto a lightly floured surface and knead for about 10 minutes, until it becomes very smooth and elastic. Shape it into a ball, place it in a bowl brushed with oil, and cover it. Let it rest at room temperature for 1 hour.

Melt the butter in a skillet over medium heat. Add the breadcrumbs and cook, stirring often, for 2 to 3 minutes until they turn golden. Spread them out and let them cool completely.

Toss the sliced apples with lemon juice to prevent browning. Stir together the sugar and cinnamon. Soak the raisins in lukewarm water for 10 minutes, drain well, and set aside.

Dust a large tablecloth with flour and roll the dough into a rough 13 to 15 inch circle. Gently stretch it until it is paper-thin and translucent, about 24 x 30 inches. Brush half with melted butter, spread the toasted crumbs on the other half, and leave a border around the edges.

Top with apples, raisins, walnuts, and cinnamon sugar. Fold in the sides, then lift the tablecloth to roll the strudel up snugly, jelly-roll style. Move it to a parchment-lined baking sheet seam-side down, brush with the remaining butter, and bake for 30 to 40 minutes, until crisp and deep golden.

Let it cool for 15 minutes, then dust with powdered sugar and slice with a serrated knife.