If you have a smaller air fryer or are making a larger batch of meatballs, make sure you don't overcrowd the meatballs in the air fryer. Cook in batches if needed.
Preheat air fryer at 380°F/193°C for about 5 minutes.
In large bowl mix together all the meatball ingredients (beef, breadcrumbs, egg, Worcestershire sauce, onion powder, garlic salt, optional mustard powder, salt, and black pepper).
Lightly oil your hands and shape the meat into 12 evenly sized meatballs about the size of a heaping 1/8 cup (a medium cookie scoop also works great for forming the meatballs).
Lightly spray the basket/tray of the air fryer with oil. Add the meatballs into an even layer. Spray the meatballs with oil to lightly coat.
Air Fry at 380°F/193°C for 8 minutes, then turn the meatballs. Spray meatballs with additional oil if they look dry.
Continue to Air Fry at 380°F/193°C for another 2-4 minutes or until cooked through and to your preference.
Serve on toothpicks or skewers for appetizers, or add a tomato sauce and serve on pasta, rice, or in a sandwich.