Preheat the oven to 450°. Season the pork with salt and pepper. Heat a heavy, medium ovenproof skillet over medium-high heat. Add 1 tablespoon oil, then the pork; cook, turning, until browned, about 2 minutes. Transfer to the oven and roast until a thermometer registers 150°, about 10 minutes. Transfer to a cutting board and let rest for 10 minutes; cut into 1/2-inch cubes.
In a small skillet, heat the remaining 1 tablespoon oil over medium heat. Add the onion and cook, stirring, until softened, about 8 minutes.
In a large bowl, whisk together the hoisin sauce, honey, sesame oil and soy sauce. Stir in the onion and the pork and its juices.
Preheat a panini press. Divide the pork mixture evenly among the roll bottoms, then cover with the tops. Working in batches if necessary, grill until browned and crisp.