Brush one side of one slice of mozzarella cheese with water then stack a second slice on top and repeat the brushing and stacking until all four slices are sealed together.
Add the flour to one shallow bowl.
Whisk the eggs in a second shallow bowl.
Add the breadcrumbs to a third shallow bowl.
Dredge the cheese in the flour, coating it on all sides, then shake off any excess.
Dip the cheese in the eggs, shaking off any excess, then coat it with the breadcrumbs. Repeat the egg and breadcrumb steps so that the cheese has two layers of coating.
Add about 1/2 inch of oil to a skillet set over medium heat. Line a plate with paper towels.
Once the oil is hot (test this by dropping a breadcrumb into the oil; it should sizzle immediately), add the coated cheese. Pan-fry it on one side until it is golden brown, about 1 minute. Flip the cheese once and continue pan-frying an additional 1 minute. Using a spatula, transfer the cheese to a paper towel-lined plate and immediately season it with salt.
Serve immediately with your choice of toppings.