In a large bowl, dissolve the yeast and sugar in warm water. Let stand for 5-10 minutes, or until foamy.
Add the flour, salt, and olive oil to the yeast mixture. Stir until a shaggy dough forms.
Turn the dough out onto a lightly floured surface and knead for 5-7 minutes, or until smooth and elastic. If the dough is too sticky, add a little more flour, 1 tablespoon at a time.
Lightly grease a large bowl with olive oil. Place the dough in the bowl, turning to coat. Cover with plastic wrap and let rise in a warm place for 1-1.5 hours, or until doubled in size.
While the dough is rising, prepare the garlic butter. In a small bowl, combine the melted butter, minced garlic, Italian seasoning, garlic powder, and red pepper flakes (if using).
Grate the Parmesan cheese and shred the mozzarella and provolone cheeses. Set aside.
Prepare your chosen fillings by cooking or chopping them as needed.
Preheat oven to 375°F (190°C). Grease a large baking sheet or pizza pan.
Punch down the risen dough to release the air. Turn it out onto a lightly floured surface.
Roll the dough into a large rectangle, about 12x18 inches.
Brush the entire surface of the dough with the garlic butter.
Sprinkle the Parmesan cheese evenly over the garlic butter.
Layer the mozzarella and provolone cheeses over the Parmesan cheese.
Scatter your chosen fillings evenly over the cheese.
Starting from one of the long sides, tightly roll the dough into a log.
Pinch the seam to seal it.
Using a sharp knife or pizza cutter, cut the log into 1-inch thick slices.
Place the slices, cut-side up, onto the prepared baking sheet, arranging them close together.
Bake for 20-25 minutes, or until the bread is golden brown and the cheese is melted and bubbly.
Let cool slightly before serving. Garnish with fresh parsley, if desired.