Preheat oven to 400 degrees.
Place yam cubes on a baking sheet and drizzle with 2 teaspoons olive oil, toss to coat then liberally sprinkle with salt and black pepper.
Spread in single layer on baking sheet.
Bake for 20 minutes, turning halfway through cooking.
Remove from oven and transfer to a plate.
Place in refrigerator to chill for about 30 minutes.
While yams are cooling, whisk together 1 cup yogurt, 2 teaspoons mustard, 1 teaspoon ¼ dill, ¼ teaspoon garlic, and 1 Tablespoon plus 1 teaspoon pickle juice in a large bowl.
Fold in 1 cup chopped celery, 1 bunch chopped green onions, 1 chopped red pepper and ½ cup green olives.
Gently fold in chilled yams and return to refrigerator to chill for 30 minutes. Taste to determine if more salt and pepper needs to be added before serving.