Heat wok or large saucepan over high heat. Add half of the oil and swirl to coat. Heat until hot.
Sauté one third of the steak for 1 to 2 minutes or until browned and just cooked. Transfer to a plate.
Repeat with remaining two batches.
Heat remaining oil. Add onion, garlic, capsicum, chili and pepper.
Stir-fry for two minutes, or until onion begins to soften. Add mushrooms and stir-fry for a further two minutes.
Return steak to the wok. Add remaining ingredients.
Bring sauce to the boil and allow to thicken for 1 minute before serving.
Serve the gluten-free free garlic pepper steak with white rice or rice noodles.