Preheat the oven to 450°F. Line an 11x17-inch baking sheet with parchment paper.
Rinse the zucchini under water. Trim off one of the ends of the zucchini and shred it on a grater.
Remove excess water from the grated zucchini by wrapping it in a cheesecloth or paper towel and tightly squeezing. You want to make sure to get as much moisture out of the zucchini as you can.
Add the drained zucchini to a large mixing bowl.
To the bowl with the grated zucchini, add the grated and drained onions, garlic, white cheddar cheese, eggs, flour, salt, and pepper. Mix well.
Using a spatula, spread the zucchini mixture out onto the lined baking sheet in an even layer. The layer will be very thin (no more than ½-inch thick). If it is too thick, it will take longer to bake and get too crispy.
Bake for 30 minutes, or until the edges are golden brown.
Remove from the oven and lower the oven temperature to 425°F.
Flip the zucchini breadsticks over. To flip, first, use a spatula to loosen up the edges. Place another piece of parchment paper over the top of the zucchini mixture and top with another 11x17-inch pan. Using hot pads, hold the edges of the pans together tightly and carefully flip over the zucchini. (You could also use a couple of spatulas to carefully flip over the breadsticks onto the same baking sheet.)
Top the breadsticks with shredded mozzarella cheese, parmesan cheese, and Italian seasoning.
Bake for an additional 15 minutes, or until the cheese is melted and the crust is crispy.
Cut the bread into strips and garnish with parsley. Serve warm with marinara sauce for dipping.