Stir sour cream, yogurt, mustard, dill, salt, pepper in large bowl. Cook potatoes in pot of water 10 minutes. Add spinach. Cook 2 minutes, until potatoes are tender. Drain. Add to bowl; fold into dressing.
Prepare grill or heat broiler. Spread each fillet with 1 teaspoon mustard. Sprinkle evenly with the salt, pepper and dill. Drizzle oil over fillets.
Grill or broil salmon 4 to 6 inches from heat for 8 to 10 minutes or until cooked through. Remove from heat; let stand 5 minutes. Serve with dilled potatoes. Makes 4 servings.
