Adjust rack to middle position and preheat oven to 325°F.
Place salmon, skin side down, on a parchment-lined sheet pan. Sprinkle generously with Kosher salt and then some freshly ground black pepper, to taste. Sprinkle evenly with garlic powder and dried oregano, then rub salmon all over with olive oil. Roast for 20-23 minutes, until just cooked through and tender. (TIP: If doubling the recipe, cook for a few minutes longer)
When salmon is done cooking, raise oven temperature to 400°F. Let salmon cool to room temperature, then flake into medium-sized pieces. Discard the skin.
While the salmon cooks, place the potatoes in a medium pot and cover with salted water. Bring to a boil over high heat, then add in baking soda, and cook for 8-10 minutes, until cooked through but not super soft.
Drain water from potatoes. Close potatoes in the pot with a tight-fitting lid and shake vigorously to rough up the potatoes. Smash remaining potatoes that haven’t broken apart, using the bottom of a wooden spoon or a knife. Mix with avocado oil and season with Kosher salt.
Prepare a sheet pan (you can use the same sheet pan as the salmon) drizzled with avocado oil. Spread the potatoes onto the sheet pan. Roast for 40-50 minutes, flipping the potatoes once or twice in between, until browned and crispy. Let cool slightly until warm.
In a large bowl, toss the lettuce, red onion, flaked salmon, warm crispy potatoes, and as much of the Tartar Dressing as you’d like. Season with Kosher salt and freshly ground black pepper and toss again. Sprinkle with fresh dill and serve immediately.