Prepare Vegetables: In a medium-sized bowl, combine red potatoes, carrots, bell peppers, and red onion. Season with salt and pepper, and toss with olive oil.
Assemble Foil Packets: Cut four 18x12-inch pieces of heavy aluminum foil. Evenly distribute the vegetable mixture on each piece of foil. Top the vegetables with the steak cubes.
Make Garlic Herb Butter: In a small bowl, mix together the butter, parsley, garlic, rosemary, thyme, salt, and pepper. Divide the mixture evenly and place on top of the steak in each foil packet.
Seal and Cook: Double fold the top and ends of each piece of foil, leaving space for steam. Grill the packets over medium heat for about 15 minutes, or until the steak is cooked through and the veggies are tender. Alternatively, bake in a preheated 400°F oven for 25-30 minutes, opening and broiling at the end for a slight char.
Serve: Carefully open the foil packets and enjoy your Butter Garlic Herb Steak Foil Packet meal!