In a large bowl, combine the beef, cheddar, mustard, salt, onion powder, and pepper. Gently form the meat into 8 equal patties, about 1/2 inch thick. Press your finger in the center of each patty to create a dimple (this will help maintain their flat shape when they cook).
For the special sauce
In a medium bowl, combine the mayonnaise, ketchup, mustard, pickle juice, onion powder, garlic powder, and paprika and mix until smooth.
Preheat the air fryer to 400 F.
Working in batches, arrange a single layer of sliders in the air fryer basket. Cook, flipping halfway, to your desired doneness, 8 minutes for medium.
To serve, place 2 lettuce halves on each plate and top each with a slice of tomato, a slider, onion, special sauce, and pickles. Serve immediately!