In a large mixing bowl, combine the flour, yeast, salt, and sugar. Add the olive oil and water, and mix by hand just until a cohesive dough forms. Cover with plastic wrap and let rest for 30 minutes.
Lift four corners of the dough and fold them into the center. Cover and let rest for another 30 minutes. Repeat the folding process once more, then let rest again for 30 minutes.
Transfer the dough to a lightly floured surface, making sure it is dusted on all sides. Divide into three equal portions. Roll each into a rectangle, scatter walnuts, Gouda, and rosemary on top, then press gently to secure. Fold one half of the rectangle toward the center, then fold the other half over it. Press lightly to flatten and cut slits into the surface. Repeat with the remaining portions.
Preheat the oven to 450°F (230°C). Arrange the loaves on a baking sheet lined with parchment. Brush with olive oil, sprinkle with semolina, and bake for 15 minutes, until deeply golden and the cheese is bubbling. Cool slightly on a wire rack before serving.