Cut the block of mozzarella crosswise into 6 equal pieces. Then, cut each sixth lengthwise into 3 pieces, making sticks about 3½ to 4 inches long and ¾-inch wide.
Place the flour in a shallow bowl. In another shallow bowl, whisk the eggs with ¼ cup (60mL) of water. In a third shallow bowl, mix the breadcrumbs, garlic powder, salt, and black pepper.
Working in batches, dredge the sticks of cheese in the flour, then the egg, then thoroughly coat in breadcrumbs. Place the breaded cheesesticks on a small, parchment lined baking sheet.
Once all of the cheese sticks are coated, dip them in the egg mixture once again, then the breadcrumbs, pressing to coat. Return them to the same sheet tray. Place the tray in the freezer for 45 minutes to 1 hour.
Meanwhile, fill a medium saucepan with 1½ inches of vegetable oil. Place over medium heat until the temperature on an instant-read thermometer reaches 350°F. Working in batches, fry 4 to 5 mozzarella sticks at a time, turning once to brown evenly, for 2 to 2½ minutes. Remove with a slotted spoon or spider, and transfer to a paper towel-lined plate. Repeat with the remaining mozzarella sticks.
Serve the mozzarella sticks immediately with warm marinara sauce.
Notes
Coat the mozzarella sticks in breadcrumbs twice. This will both create a crispier exterior and help prevent the cheese from leaking out in the frying oil. And don't be afraid to really press the crumb mixture into the sticks to create a nice, thick layer.
It's important to adjust the heat of the stove as needed while frying. The oil temperature needs to stay at 350°F for the best results. If the oil gets too hot, the mozzarella sticks will brown too quickly, burning the exterior before the cheese in the center melts. If it is too cool, the sticks will absorb excess oil, making them greasy and not as crispy. A deep frying/candy thermometer or instant-read thermometer is your best friend here.
Be careful when adding the sticks to the oil. Dropping them from a height will cause the oil to splatter! Gently slide the frozen sticks into the hot oil, or use a slotted spoon or spider to assist you. While you're at it, take extra precaution and wear long sleeves, long pants, an apron, and close-toed shoes in case the oil does splatter.
Drain the fried mozzarella sticks well. This will prevent them from tasting greasy. Also, don't cover them with foil or plastic wrap when they're hot—this will cause condensation to form and make the beautifully crisp exterior turn soggy and sad. If you need to keep them warm, place them on a wire rack in a 200°F oven.