Preheat your oven to 400°F (200°C). Line a large baking sheet with foil for easy cleanup.

Tear off 4 large sheets of heavy-duty aluminum foil (about 12x18 inches each). Lightly spray the center of each foil sheet with nonstick cooking spray if desired.

Thinly slice the onions and halve the baby potatoes (or cut larger potatoes into 1-inch chunks).

Pat the beef dry with paper towels and slice into strips if it isn't already thinly sliced.

In a large bowl, toss the potatoes and sliced onions with the olive oil, steak seasoning, and a pinch of salt and pepper if needed.

Divide the seasoned onion-and-potato mixture evenly among the four foil sheets, piling it in the center of each.

Top each pile with an equal portion of the sliced beef, spreading it out slightly so it cooks evenly.

Bring the long sides of the foil up and together over the filling and fold them down tightly to seal. Roll up the short ends to form snug packets, leaving a little room inside for steam circulation.

Place the packets on the prepared baking sheet. Bake at 400°F (200°C) for 30–35 minutes, or until the potatoes are tender and the beef is cooked through.

If preferred, open the packets for the last 5 minutes to reduce steam and slightly crisp the beef. Carefully open one packet and test a potato for doneness. If needed, reseal and bake an additional 5–10 minutes.

Remove from the oven and let the packets rest for 3–5 minutes before serving. Serve directly in the foil packets or transfer contents to shallow bowls, spooning juices over the top.