Preheat a grill or grill pan on medium heat. Season both sides of the steak with steak seasoning, salt and pepper.
Grill the steaks on both sides to your desired temperature using a thermometer. (see notes below) Once cooked set aside to rest while the sauce is made.
Heat the oil on medium heat in a nonstick pan. Saute the garlic and shallot for 2 - 3 minutes. Cook for 2 minutes and then add the mushrooms. Saute until the mushrooms are soft then add in the butter.
Slice the steak against the grain. Spoon the mushroom mixture over the steak. Garnish with parsley.