Prepare grill.
Prick each potato several times with a fork and wrap individually in aluminum foil. Place on grill 20 to 25 minutes, or until fork tender.
Meanwhile, brush salmon with olive oil and mustard. Grill 5 minutes on one side, turn, and continue grilling 5 to 7 minutes or until fish flakes easily to fork or is no longer translucent. Top each potato with 2 tablespoons each of sour cream and salsa, and serve with cooked fish.