The best roast pork for this sandwich is one that's both slightly sweet and garlicky too. Latin-style is best; alternatively, use a Chinese version or a baked, cured or smoked ham.
Preheat the oven to 400°. In a food processor, combine the parsley, olives, garlic, jalapeños and vinegar. Process to a coarse paste. Add the olive oil and process briefly until thick. Scrape the olive paste into a small bowl and season with salt and pepper.
Spread a thin layer of ketchup on the bottom half of the rolls. Layer one-fourth of the pork, sliced onion and Provolone on top. Set the sandwiches on a baking sheet; bake for about 2 minutes, or until the Provolone melts. Spread 2 tablespoons of the olive paste on the top halves of the rolls. Assemble the sandwiches, cut them in half and serve.