Preheat oven to 400°F (200°C) and line a baking sheet with parchment paper.
Toss halved potatoes with 2 tbsp olive oil, half the salt, and half the pepper, then spread evenly on the pan.
Roast potatoes 15 minutes until starting to turn golden.
In a bowl, mix melted butter, garlic, lemon juice, lemon zest, oregano, remaining salt, and pepper.
Push potatoes slightly aside and place salmon fillets on the same pan.
Brush salmon generously with lemon butter mixture.
Roast 12–15 minutes more until salmon flakes easily and potatoes are crispy.
Garnish with parsley and serve immediately.
