In a large mixing bowl, mix together cheddar, mozzarella, onion, egg, cream cheese, sour cream, hot sauce, salt, and pepper until well-combined.
Fill each jalepeño half with the cheese mixture.
In a small wide shallow bowl, stir together panko and melted butter until the breadcrumbs are moistened. Dip the jalapeños, cheese-filled side down, in the crumbs to coat evenly.
Add to the air fryer in an even layer. Cook for 7 minutes at 375˚F. You will likely have to cook these in batches, depending on the size of your air fryer. Make sure to only load your air fryer with enough to be in a single layer - do not layer them on top of each other!
Serve warm.