Preheat oven to 350 °F. Coat a large baking sheet with cooking spray.
Combine sugar, cornstarch, egg white, vanilla and lemon zest in a small bowl; stir gently until well combined. Gently fold in ricotta with a rubber spatula until just combined. Gently fold in raisins. Set aside.
Combine oil and butter in a small bowl. Unroll phyllo sheets onto a clean, dry surface; cover with wax paper and then a slightly damp tea towel to prevent the dough from drying out.
Lay one sheet of phyllo on prepared baking sheet. Sprinkle with 1/2 teaspoon of oil mixture and spread it around with a pastry brush. (Not all the dough will be covered.) Sprinkle with 1/2 teaspoon breadcrumbs. Repeat with 6 more sheets of phyllo, aligning each sheet over the previous ones. Lay the final phyllo sheet on top; do not sprinkle with oil, but sprinkle with remaining breadcrumbs; reserve remaining oil/butter mixture.
Gently spoon the cheese filling in a long, 12-by-2-inch mound along one long edge of the phyllo layers, leaving a 3-inch border between the mound and the short edges of the phyllo. Fold up the long edge and loosely roll up the strudel. (Do not roll too tightly; the filling will expand during baking.) Set the strudel, seam-side down, on the baking sheet. Fold and tuck the open ends securely, but not tightly, beneath the roll.
Brush strudel with remaining oil mixture. Make four short (1-inch) diagonal slashes along the top of strudel with a sharp paring knife, to allow steam to escape. Bake until the phyllo is golden brown, 35 to 40 minutes. Carefully transfer strudel to a wire rack and allow to cool completely.
Just before serving, dust strudel with confectioners' sugar and slice with a serrated knife. Pool a spoonful of Raspberry Coulis on each dessert plate and top with a slice of strudel.
To ensure the smoothest texture for your strudel filling, check the labels on the part-skim ricotta in your supermarket and choose one that does not contain gums or stabilizers.Part-skim ricotta has about half the fat of whole-milk ricotta.