Preheat the oven to 450°F.

Pat the salmon fillets dry with a paper towel and season each fillet with a few pinches of salt. Place them in an ovenproof baking dish large enough to avoid crowding.

In a small bowl, add the mustard, sugar, ¾ teaspoon salt, smoked paprika, pepper, and garlic, and mix until smooth. Brush each fillet with the brown sugar mustard sauce. Bake until the salmon flakes easily and is cooked through at the thickest part, about 9 to 11 minutes. Let the salmon rest for 5 minutes before serving.

Meanwhile, in a medium mixing bowl, add mashed potatoes, cornstarch, egg, and a pinch of salt. Mix until thick and pasty. Set aside.

Heat a ¼-inch layer of olive oil in a medium skillet over medium heat. Once the oil reaches 350ºF, working in batches, spoon about ¼ cup of the potato mixture into the hot oil, then gently press each potato round into a 3-inch patty.

Cook until golden brown, flipping halfway, about 5 to 6 minutes total. Transfer the cooked potato pancakes to a paper towel-lined plate and season with flaky salt.

Pour off most of the oil, leaving about 1 tablespoon in the skillet. Over medium heat, add spinach and a pinch of salt, mixing until wilted and tender, 1 to 2 minutes. Add the juice from 2 lemon wedges and a few cranks of black pepper. Taste and adjust the seasoning, if needed.

Smear each plate with a dollop of Greek yogurt, then carefully place the potato pancakes on top. Place the lemon spinach and glazed salmon fillets to the side of the pancakes, spooning any excess sauce over the fillets. Garnish with freshly ground black pepper and lemon wedges.