Step 1 In a medium bowl, whisk together the flour, semolina and baking powder.
Step 2 In a medium saucepan, bring the oil and 1 cup water to a boil. Lower the heat and stir in the flour mixture with a wooden spoon, stirring constantly and pressing the dough to dissolve any lumps. Continue stirring until the dough is of uniform consistency. Remove from heat and cool the dough until it is warm.
Step 3In a small bowl, mix the filling ingredients: whisk together one-fourth cup sugar, the sesame seeds, walnuts and cinnamon and set aside.
Step 4Heat the oven to 350 degrees. Grease an 8-inch or 9-inch round or square baking pan and press half of the dough evenly onto the base of the pan. Sprinkle the filling evenly over the dough, and pat it down gently into the dough. Press the remaining dough over the filling to evenly cover (this can be done with a damp spatula). Cut the dough into squares, and sprinkle the top with a light covering of sesame seeds.
Step 5Bake until the cake is golden, but not browned, about 50 to 60 minutes (rotate halfway for even baking). Remove from the oven and cool slightly.
Step 6While the bars are cooling, prepare a finishing syrup. In a medium saucepan, combine the remaining three-fourths cup sugar, one-half cup water and lemon juice. Cook over medium-low heat, stirring often with a wooden spoon till the syrup dissolves and begins to thicken, about 5 to 6 minutes. Pour the syrup over the warm cake and bring to room temperature before serving. May be covered and kept at room temperature overnight or covered and stored in the refrigerator. Bring to room temperature before serving.