1 cup plain nonfat yogurt
2 shallots, minced
2 Tbsp. chopped fresh dill
2 Tbsp. extra-virgin olive oil
2 tsp. Dijon mustard
1 tsp. grated lemon zest
2 Tbsp. fresh lemon juice
1/4 tsp. salt
8 cups baby salad greens
3 medium beets, peeled and shredded
1 cup very thinly sliced radishes
2 medium carrots, peeled and shredded
1/3 cup chopped unsalted pistachios
1/4 tsp. freshly ground black pepper, or to taste (optional)