Preheat the grill to medium-high, about 375°F (190°C).
Cut four large sheets of aluminum foil, one for each fillet.
Brush each cod fillet with olive oil on both sides.
Season both sides of each fillet evenly with garlic powder, dried oregano, paprika, salt, and black pepper.
Place each seasoned fillet on a sheet of foil and top with lemon slices.
Fold the foil over each fillet and seal the edges to make a tight packet.
Grill the foil packets for 10–15 minutes, until the cod is opaque and flakes easily with a fork.
Carefully open the packets, garnish with chopped fresh parsley, and serve immediately.