Prepare the salmon: Pat the salmon fillets dry with paper towels. Let them sit at room temperature for 10 minutes. Rub the vegetable oil evenly over all sides of each fillet.
Make the cajun seasoning: Mix together the garlic powder, ground cumin, smoked paprika, cayenne pepper, dried oregano, dried thyme, sea salt, and black pepper in a small bowl.
Season the salmon: Generously sprinkle the cajun seasoning over all sides of the salmon fillets, pressing gently to help it stick. Let the seasoned salmon rest for 10 minutes.
Preheat the grill: Heat your grill or grill pan to medium heat (around 180°C). Lightly oil the grill grates using a folded paper towel dipped in oil.
Grill the salmon: Place the salmon fillets on the grill, skin side down if using skin-on salmon. Cook for 5 minutes without moving. Flip carefully and cook for another 4-5 minutes on the second side.
Check for doneness: The salmon is done when it reaches an internal temperature of 63°C (145°F) and flakes easily with a fork. It should be opaque throughout with just a hint of translucency in the centre.
Rest and serve: Transfer the salmon to a serving plate and let rest for 2-3 minutes. Serve immediately with fresh lemon wedges.