Cut the sirloin steak into pieces approximately 1 1/2 inches by 1 inch.
Place the oil, ground black pepper, salt, and soy sauce in a large mixing bowl.
Whisk the ingredients together until fully combined.
Add the steak pieces to the bowl.
Toss the steak pieces thoroughly until they are evenly coated with the seasoning mixture.
Preheat the air fryer to 400°F.
Arrange the steak pieces in the air fryer basket in a single layer. Avoid overcrowding the basket to ensure even cooking.
Cook the steak bites at 400°F for 8 minutes, or until cooked to the desired level of doneness.
For a more rare result, cook the steak bites for approximately 6 minutes.
For a medium-well result, cook the steak bites for approximately 12 minutes.
Remove the steak bites from the air fryer and allow them to rest briefly before serving.
Serve as a main dish with steamed rice, vegetables, noodles, or salad.
Alternatively, serve as an appetizer with preferred dipping sauces.