Once butter melts, add steak. Coat steak with parsley, salt, and pepper. Cook steak for 5-7 minutes or to desired doness. Flip halfway.
Take steak out to rest on a plate. Add chopped peppers and onion to skillet. Add a little olive oil if needed. Cook vegetables on medium until soft stiring throughout.
Cut steak into bite sized pieces and add back to skillet. Stir until combined. Add more parsley, garlic salt, or pepper if needed.