Rub steak with salt, pepper, garlic powder, and onion powder.
Heat oil in a large skillet over medium-high heat. Add steak and cook, fl ipping occasionally, until browned and cooked through, about 3-5 minutes. Remove from heat and set aside.
Bring 1 1/2 cups water to a boil in a saucepan over high heat. Whisk together Au Jus Gravy Mix and remaining water together in a small bowl. Pour gravy mixture into boiling water, whisking constantly until completely smooth and thickened, about 1 minute. Remove from heat and add steak to gravy, stirring to coat.
Divide steak evenly among hoagies. Top with 2 slices of cheese.
Place sandwiches onto a parchment-lined sheet tray and broil on low until lightly toasted and cheese is melted, about 2-3 minutes. Serve warm with remaining gravy.
