Select 3 bowls large enough to hold each ½ sandwich, and prepare your dredging station.
Place the flour in the first bowl. In the second bowl, crack the eggs and whisk to fully combine. In the third bowl, place the breadcrumbs and parmesan cheese and mix together. Set aside.
To prepare the sandwiches, place the two bottom bread slices down, and top each with one layer of mozzarella, dividing it evenly between the two sandwiches. The mozzarella should not hang over the edges of the bread.
Season the fresh mozzarella with salt and pepper to taste. Place the top layer of bread down and gently press the sandwiches so that they stick together. (Optional: cut the garlic clove in half and rub one inside layer of the bread with the fresh garlic). Carefully cut each sandwich in half on the diagonal, creating 4 triangles.
Dredge the sandwich triangles in the flour first, shaking off any excess.
Next, dip the sandwiches in the egg, making sure that each side is evenly coated and soaks up some of the egg.
Finally, press the sandwich gently into the parmesan breadcrumbs. The sandwiches should be completely sealed with breadcrumbs on all sides. If necessary, dip any open edges in the egg mixture again, and press into the remaining bread crumbs. This will ensure the mozzarella doesn’t leak out of the sandwich as it fries in the oil.
While the sandwiches rest for about 10 minutes, heat approximately 3-inches of oil over medium heat, until it reaches 350°F. Your pan should be large enough to fry 2 triangles at a time, and deep enough to allow space for the oil to safely expand while the sandwiches are frying.
Fry each triangle for about 1 ½ minutes per side, or until golden brown. After the sandwich is golden on both sides, transfer to a paper towel lined plate to allow some of the oil to drain. Season with a sprinkle of salt if desired.
Serve each triangle while still warm, with a side of warmed marinara sauce for dipping.