Cut the potatoes in like-sized wedged, either halved or quartered. Toss with oil and generous pink of flaky salt on large baking sheet. Roast in the oven at 375 for 40 mins.
On a small baking sheet, season flesh side of salmon with salt and rest salmon at room temp while potatoes roast.
In a medium bowl, combine mayo, parsley, dill, lemon juice and garlic.
Once the potatoes have roasted, remove from the oven and push potatoes to either edge of the baking sheet. Place the salmon, skin side down on the hot sheet. Top each filet with 1-2 tbsp of mayo and spread to the edge.
Return sheet pan to the oven and cook until internal temp of salmon reads 120 (med rare) or desired doneness (roughly 13-15 mins). Remove from oven, let rest 5 mins before serving.