Preheat a grill to medium. Shape each piece of pizza dough into a ball. Drizzle 1 tablespoon olive oil on each of 2 rimmed baking sheets, place 1 dough ball on each baking sheet and turn to coat in the oil. Place a metal cooling rack upside down on the grill perpendicular to the grill grates (or use a grill basket); brush the rack with the remaining 1 tablespoon olive oil. Working in batches, grill the pineapple, scallions and ham, turning as needed, until lightly charred, 5 to 8 minutes per batch; transfer to a plate as each batch is done. Cut the ham slices in half, if desired. Using tongs, remove the cooling rack from the grill. Pat and stretch or roll each dough ball into an approximately 8-by-12-inch oval. Carefully place each piece of dough directly on the grill and cook until marked and golden, about 5 minutes. Flip the crusts and top evenly with the cheese, ham, scallions and pineapple. Continue grilling until the cheese melts and the crust is cooked through, about 6 more minutes. (If the crust is browning too quickly, slide the pizzas to the outer edge of the grill.) Transfer the pizzas to a cutting board and cut into pieces.