If you don't have curry powder, use a mix of 1 teaspoon each cumin, coriander and turmeric and 1/2 teaspoon each ground mustard and ground ginger. Combine the yogurt, curry powder and lemon juice in a large bowl and season with salt and pepper. Add the chicken, scallions, apples and carrots and mix until combined. Adjust the seasonings. Butter the rolls and toast on a hot griddle. Fill with lettuce, chicken salad and a sprinkle of almonds and crystallized ginger. Serve with chips. The chicken salad can be covered and refrigerated for a make-ahead meal.