Cut each mozzarella string cheese stick in half to create 24 shorter pieces, then place them on a parchment-lined baking sheet and freeze for at least 1 hour.
Set up three shallow bowls: one with flour, one with beaten eggs, and one with breadcrumbs mixed with Parmesan cheese, garlic powder, oregano, and salt.
Working with frozen cheese sticks, dredge each in flour, dip in egg, coat with breadcrumb mixture, then dip in egg again and coat with breadcrumbs a second time for a double coating.
Place double-breaded mozzarella sticks back on the baking sheet and freeze for an additional 30 minutes to ensure they stay intact during cooking.
Spray the air fryer basket with cooking spray and arrange frozen mozzarella sticks in a single layer without touching, then spray the tops lightly with cooking spray.
Air fry at 390°F for 6-8 minutes until golden brown and crispy, working in batches if necessary, and serve immediately with warm marinara sauce.