Cut 8 sheets of aluminum foil, approximately 14" x 10" each. If using thinner foil, double the layers for added durability.
Lay out 4 foil sheets and lightly coat them with nonstick cooking spray.
Divide the onions, potatoes, and green peppers evenly among the 4 foil sheets, placing the vegetables in the center of each packet and leaving about 3 inches of space around the edges.
Crumble the raw ground beef into 1-inch pieces and distribute evenly over the vegetables.
Sprinkle each packet with 1 teaspoon steak seasoning and ¼ teaspoon black pepper.
Top each packet with a second sheet of foil. Fold and seal the edges tightly to create secure packets, making sure no steam can escape during cooking. If using thinner foil, double the top layer as well.
Cook according to the instructions below until the vegetables are tender and the beef is fully cooked.
Carefully open the packets and place a slice of cheese on top of each serving. Loosely cover the packets and let them sit for 1 to 2 minutes, or until the cheese has melted.