Preheat your air fryer to 200℃ - 390℉ for 5 minutes. This step is important for this recipe to ensure the steak gets a nice even browning.
Slice the steak into 1.5" - 4 cm cubes. If you want to make them larger, you need to adjust the cooking time accordingly.
Give the mushrooms a quick wash and slice them to a similar size to ensure they cook in the same amount of time as the steak bites.
Season the steak bites and sliced mushrooms with salt and pepper, and place them into the air fryer basket. You don't need to use oil for the basket for this recipe.
Air fry them for 5-6 minutes.
While the steak and mushrooms are in the air fryer, prepare your garlic butter.
Heat the butter in a large skillet or heavy-based pan over medium-high heat until melted.
Add the garlic, thyme, and chili, and cook until fragrant, about 30 seconds.
Next, add the steak bites to the skillet and give them a good shake. Toss everything together for about a minute, then serve immediately with your favorite side dishes.