Preheat grill to medium-high heat.
Make a batch of this Garlic Butter. Divide in half and melt in the microwave for 20-30 seconds. Combine the potatoes and the onions in a bowl. Pour the melted garlic butter over the top; set aside.
Spread the remaining non-melted butter over the steak to evenly coat.
FOR WELL DONE STEAKS:
Slice your fillet into 1-inch thick slices (the smaller the pieces, the more cooked through it will be -- be careful not to slice them too small or they will dry out).
FOR MEDIUM RARE STEAKS:
Cut your fillet into 4-6 large pieces.
TO COOK:
Tear four or six 15-inch (40cm) pieces of heavy duty foil and arrange on your kitchen counter or bench top. Divide steaks and potatoes among the top half of the foil sheets. Sprinkle with parsley, and season with salt and pepper
Fold up the sides of the foil first over the steak and potatoes, then fold up the entire bottom half of the foil over the ingredients to join the ends. Fold down to seal, pressing the seal tightly to prevent any juices from spilling out.
Place foil packets on the grill, cover and cook for 7 minutes on one side. Flip and cook on the other side for a further 5 minutes, until potatoes are cooked through, (about 12 minutes all together). CAREFULLY open the foil packets (being careful of the escaping steam). Sprinkle the cheese over the potatoes, and loosely tent with the foil again to allow the cheese to melt through for a further 3 minutes while still on the grill.
Top the potatoes with the cooked bacon, garnish with the scallions (or green onions), and season with a little extra salt and pepper, if needed.
Recipe Notes
*It's very important you use a cut of steak that will stay tender during the cooking process. Eye fillet, ribeye, porterhouse, top sirloin, etc.
**Substitute cheddar/mozzarella with Monterey Jack cheese if you prefer.
For Stove Top:
If you can, use a cast iron skillet or a heavy based pan. Preheat skillet over medium heat. When foil packs are ready, place them in the hot, preheated skillet to cook for 7 minutes, covered (you may need to do them in batches of two). Flip and cook for a further 7 minutes (covering again), until done.
For Oven:
Preheat oven to 220°C | 430°F. Prepare foil packs; place packs on a baking sheet/tray, and bake for 20 minutes in the hot oven. Flip packs and cook for a further 10 minutes, or until cooked to your liking. OPTIONAL: open foil packs being careful of trapped steam, and broil for 3-4 minutes, until charred