Preheat the oven to 425°F. Line a sheet tray with parchment paper for easy cleanup.
Cook the frozen garlic Texas Toast according to the package instructions. Typically, bake for 8 minutes, flipping halfway through for even browning.
While the toast is baking, prepare the au jus. In a saucepan, whisk together the au jus gravy mix and 3 cups of cold water. Bring to a boil, then reduce heat and simmer according to the package directions until fully dissolved and slightly thickened.
Once the au jus is ready, add the sliced deli roast beef to the pot and warm gently in the au jus, making sure the beef is fully heated through without overcooking.
After the Texas Toast has finished baking, place a half slice of provolone cheese on each piece of toast.
Evenly distribute the warmed roast beef slices over the cheese-topped toast.
Place the remaining half slices of provolone cheese on top of the roast beef to fully cover each toast.
Return the assembled toasts to the oven and bake for 3 to 5 minutes, or until the cheese is completely melted and bubbly.
Remove from the oven and garnish with dried parsley if desired.
Serve immediately with warm au jus on the side for dipping.