Peel and chop the Yukon Gold potato into 1-inch cubes.
Place the potato cubes in a pot of salted water, bring to a boil, and cook for 12-15 minutes until fork-tender.
While the potatoes cook, pat the salmon fillet dry with a paper towel and season with half of the sea salt and black pepper.
In a small mixing bowl, combine the Dijon mustard, chopped parsley, chopped dill, and garlic powder to create the herb paste.
Heat the olive oil in a non-stick skillet over medium-high heat.
Place the salmon in the skillet skin-side up and sear for 4 minutes until a golden crust forms.
Flip the salmon and spread the herb-mustard paste evenly over the seared top.
Reduce heat to medium and continue cooking for 3-4 minutes until the salmon is opaque and flakes easily.
Drain the cooked potatoes and return them to the warm pot.
Add the Greek yogurt, lemon juice, and the remaining sea salt and pepper to the potatoes, mashing until completely smooth and creamy.
Transfer the mashed potatoes to a plate and top with the herb-crusted salmon fillet.