Use a sharp knife to dice the chicken into ¼" thick pieces. Place in a large bowl.
To the same bowl, add the eggs, mozzarella, Parmesan, breadcrumbs, mayonnaise, green onions, garlic, salt and black pepper. Stir until well combined. Cover with plastic wrap and place in the fridge for at least 2 hours or overnight.
Preheat oven to 250°F and place a wire rack on top of a baking sheet. Add 1 tablespoon of oil to skillet over medium heat. Scoop up ¼ cup of the mixture per fritter and drop into skillet. Use a spatula to flatten into discs. When the edges of the fritters are brown and crispy, about 3-4 minutes, flip. Cook for another 4 minutes or until browned.
Transfer cooked fritters to a paper towel-lined rack to drain and then put on wire rack in oven to keep warm while you cook the remaining fritters. Serve immediately.
Notes
Use a large cookie scoop so you can get uniform size fritters.
To avoid using too much oil, use a nonstick pan so the fritters are easy to flip.
Once you add the fritter mixture to the oil, don't move them for 3-5 minutes before flipping so they create a crispy exterior.
Leftovers will last in the fridge for 3-4 days or in the freezer for 3 months.