In a small bowl or bag, combine kosher salt, black pepper, garlic powder, and paprika. Liberally coat the duck with this mixture. Cover and refrigerate for at least 1 hour, but preferably for 6 or more hours.
Heat the oil in a heavy-duty pot, such as a Dutch oven, over medium-high heat. Add the duck and brown evenly on all sides. Add the onion and cook for an additional 5 minutes. Mix in Italian seasoning, crushed red pepper, and garlic. Cook for 2 minutes. Add wine and stir to deglaze the bits stuck to the bottom of the pot. Add vinegar and beef stock. Bring to a boil. Reduce the heat to low, cover, and simmer for several hours until the meat pulls apart easily.
Remove the duck from the pot and let cool completely. Once cooled, pull the meat off the bones or shred the breasts into bite-sized pieces. Strain the liquid from the pot and add it to the pulled meat.
To serve, reheat the meat and liquid in a skillet or Dutch oven. Add the pepperoncini and peppers and bring to serving temperature. Spoon the mixture onto rolls.