In a large mixing bowl, combine 4 cups of all-purpose flour, 2 teaspoons of instant yeast, 1 tablespoon of salt, 1/4 cup of olive oil, and 1 1/2 cups of warm water. Mix with a wooden spoon until a sticky dough forms.

Transfer the dough onto a floured surface and knead it for about 8-10 minutes until it becomes smooth and elastic.

Place the kneaded dough into a bowl lightly coated with olive oil, cover with a damp kitchen towel, and let it rise in a warm spot for about 1 hour.

While the dough rises, prepare the filling by mixing 1/2 cup of brown sugar, 2 tablespoons of ground cinnamon, and 1/4 cup of melted butter in a small bowl.

After the dough has risen, gently punch it down, roll it out into a rectangle about 1/2 inch thick, and spread the cinnamon filling evenly over the dough.

Starting from one long side of the rectangle, carefully roll the dough into a log and pinch the seams to seal it. Coil the rolled dough into a spiral shape, tucking the ends underneath.

Cover the coiled dough with a clean kitchen towel and let it rise for another 30 minutes in a warm place.

Preheat your oven to 375°F (190°C) and bake the focaccia for 20-25 minutes, or until golden brown.

Once baked, cool on the baking sheet for about 10 minutes, then transfer to a wire rack and dust with powdered sugar before serving.