In a small food processor, puree the beans with the olive oil. Stir in the Parmesan, oregano, salt and pepper.
Spread the bean mixture over the bottom half of each pita, then layer the ham and tomato slices. Top with the remaining pita halves.
Heat a large nonstick griddle. Lightly spray griddle with olive oil spray. Place each of the sandwiches, with the cheese side down, onto the hot griddle. Place an aluminum foil wrapped brick on top of each of the sandwiches. Grill for about 1 1/2 minutes on the first side. Flip the sandwiches and grill for about another minute. Remove from griddle and serve hot.