Preheat oven to 425 degrees F.
Scrub potatoes clean and poke each potato with a fork several times. Rub a little olive oil on each potato and sprinkle with a small amount of salt and pepper. Bake potatoes on a sheet pan for 45 to 55 minutes or until fork-tender.
Meanwhile, pat the salmon fillets dry with a paper towel. Place on a sheet pan and brush with dijon mustard. Sprinkle with a little salt and pepper. Bake for 10 to 12 minutes until salmon flakes apart.
Combine the yogurt, shredded cucumber, half the dill, and lemon juice in a mixing bowl. Stir till combined.
Place the potatoes on plates or in large bowls and cut open. Flatten slightly with a fork.
Scoop a quarter of the yogurt sauce onto each of the potatoes. Divide the salmon and place it on top of the potatoes. Sprinkle with a pinch of salt and pepper, drizzle with remaining olive oil, and top with remaining dill and capers.