Dissolve yeast in warm milk in a large bowl; let stand 5 minutes. Lightly spoon flours into dry measuring cups, and level with a knife. Stir in 3 cups bread flour, semolina, oil, and salt to yeast mixture to form a stiff dough. Turn dough out onto a lightly floured surface. Knead dough until smooth and elastic (about 10 minutes); add enough of remaining bread flour, one tablespoon at a time, to prevent dough from sticking.
Place dough in a large bowl coated with cooking spray, turning to coat top. Cover and let rise in a warm place (85°), free from drafts, 45 minutes or until doubled in bulk. Punch dough down; roll into a 15 x 10-inch rectangle on a lightly floured surface. Place on a large baking sheet coated with cooking spray. Place 2 ounces cheese down the center of the short length of dough; top with 2 ounces prosciutto and 2 tablespoons chives. Fold one short end of dough over filling. Place 2 ounces cheese, 2 ounces prosciutto, and 2 tablespoons chives on top of fold. Fold remaining short end over filling, pressing firmly to eliminate air pockets; pinch seam and ends to seal. Place on a baking sheet coated with cooking spray. Cover focaccia, and let rise 45 minutes or until doubled in bulk.
Preheat oven to 375°.
Uncover dough. Bake at 375° for 20 minutes. Remove from baking sheet; cool on wire rack. Cut loaf crosswise into 10 slices.