1. In a large bowl, stir yeast into water to soften. Add sugar, salt, and 1 cup flour to yeast. Beat vigorously for 2 minutes with a wooden spoon or the paddle attachment of a stand mixer. Add provolone cheese and mix until combined. Gradually add flour, a cup at a time, until dough begins to pull away from side of bowl. Transfer dough to a floured work surface. Wipe bowl clean and coat it with oil; set aside.
2. Knead dough, adding flour a little at a time if needed, until dough is smooth and elastic. Put dough into oiled bowl. Turn to coat entire ball of dough with oil. Cover with a tightly woven cloth and let rise until doubled, about 1 hour.
3. While dough is rising, prepare filling. Remove sausage from casing and break into chunks. In a large skillet over medium heat, brown sausage, about 6 to 8 minutes. Drain on paper towels. Some brands of Italian sausage are chunkier than others, so if sausage is in chunks larger than your thumbnail, chop it smaller after browning.
4. Wipe out skillet and add olive oil and onion. Cook, stirring often, over medium low heat until onions are limp and golden, about 30 minutes. Its very important to cook onions slowly to allow the natural sugars to caramelize and become sweet. Add garlic and oregano and cook for 2 minutes more. Set aside to cool.
5. Generously grease baking sheet with 1 tablespoon of butter. Melt remaining 2 tablespoons and set aside.
6. Transfer dough to a lightly oiled work surface and roll into an 18 by 12 inch rectangle. Sprinkle surface with onion mixture, peppers, sausage, and spinach, leaving an inch free of filling all around edge of rectangle. Roll dough toward the top into an 18 inch cylinder.
7. Carefully lift dough and place it seam side down on prepared baking sheet. Turn ends of loaf under to seal. Cover with a tightly woven towel and let rise for 40 minutes. About 10 minutes before baking, preheat oven to 350 degrees F.
8. Gently brush loaf with reserved melted butter and sprinkle with Parmesan cheese. Bake 45 to 55 minutes until bread is golden brown and internal temperature reaches 190 degrees F on an instant read thermometer. Immediately remove from baking sheet and cool on a rack for 20 minutes. Best served warm or at room temperature.
Source: Hannaford fresh Magazine, January - February 2007