Preheat your grill to medium-high heat (around 375°F).
Cut four pieces of aluminum foil large enough to wrap each salmon fillet and lay them out on a clean surface.
In a mixing bowl, combine olive oil, lemon juice, garlic powder, dried oregano, salt, and black pepper. Mix well.
Place one salmon fillet on each piece of foil and brush generously with the olive oil mixture.
Layer thin slices of lemon on top of each fillet for added flavor.
Fold the sides of the aluminum foil over the salmon to create a sealed packet, ensuring there are no gaps where steam can escape.
Place the foil packets on the grill and cook for about 15 minutes or until the salmon is opaque and flakes easily with a fork.
Carefully remove the packets from the grill using tongs and let them sit for a minute before opening.
Serve each fillet directly from the foil, garnished with fresh parsley if desired.