Pat the mozzarella slices dry. Spread 1 teaspoon of the ’nduja on one side of each of six slices, then top with the remaining slices to form six “sandwiches.” Set aside.
Set up your breading station: Place the flour on a plate or in a shallow bowl. Beat the eggs in a medium bowl. Place the breadcrumbs on a plate or in a shallow bowl. Season the flour, eggs, and bread crumbs with salt and pepper.
Dredge each “sandwich” first in flour, shaking off excess, then in egg, allowing excess to drip off, and finally coat in breadcrumbs. Repeat for a thicker crust, if desired, to prevent the cheese from leaking out during frying. Set aside.
In a medium frying pan or cast-iron skillet, heat 2 inches of neutral oil to 350°F. Fry the “sandwiches” in batches, until deep golden brown, 3 to 4 minutes, turning once to ensure even browning.
Drain on paper towels, sprinkle with salt, and serve hot.