Directions

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 12×18 inches each). Lightly spray the center of each with nonstick cooking spray if you’d like extra insurance against sticking.
Prep the vegetables: 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. This helps the seasoning coat everything evenly so you’re not trying to sprinkle it into each packet.
Assemble the packets: 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 a bit so it cooks evenly.
Seal the packets: Bring the long sides of the foil up and together over the filling and fold them down tightly to seal, then roll up the short ends to form a snug packet. Leave a little room inside for air to circulate so the steam can help cook everything through.
Place the packets on the prepared baking sheet and bake at 400°F (200°C) for 30–35 minutes, or until the potatoes are tender when pierced with a fork and the beef is cooked through. If your beef is very thin and you prefer it less done, you can open the packets for the last 5 minutes to let some steam escape and reduce cooking time slightly.