Combine vegetable oil and butter in a custard cup or small bowls.
Combine 3 tablespoons brown sugar, breadcrumbs, and ground cinnamon in a small bowl.
Toss the plums, 1/4 cup brown sugar, prunes, and rind in a large bowl.
Place 2 phyllo sheets on a large cutting board or work surface (cover the remaining dough to keep from drying), and lightly brush with oil mixture. Sprinkle with 2 tablespoons breadcrumb mixture. Repeat the layers with the remaining phyllo, oil mixture, and breadcrumb mixture, ending with phyllo. Lightly coat the top phyllo sheet with cooking spray. Ar-range plum mixture over phyllo, leaving a 2-inch border. Starting at short edge, roll up phyllo jelly-roll fashion. (Do not roll tightly, or the strudel may split.) Place the strudel, seam side down, on a baking sheet coated with cooking spray. Lightly spray strudel with cooking spray; sprinkle with cinnamon-sugar.
Bake at 350° for 30 minutes or until golden. Cool for 10 minutes, and remove from pan. Cut with a serrated knife.