This dish in one word: TASTY!

Preheat your oven to 400°F (200°C).

Cut four large pieces of aluminum foil, about 12×12 inches each.

In a large bowl, combine the steak cubes, sliced mushrooms, and red onion.

Drizzle the olive oil over the mixture, then sprinkle with garlic powder, dried thyme, salt, and pepper. Toss everything together until well coated.

Divide the steak and mushroom mixture evenly among the four pieces of foil.

Place a tablespoon of butter on top of each portion.

Fold the foil over the mixture and seal the edges tightly to create a packet.

Place the foil packets on a baking sheet and bake in the preheated oven for 20-25 minutes, or until the steak is cooked to your desired doneness.

Carefully open the packets (watch out for steam) and garnish with fresh parsley if desired before serving.