Chunky Chicken Salad Sandwich

Name: Chunky Chicken Salad Sandwich
Ingredients: 1 – 1 1/2 lbs. boneless, skinless chicken breast; 1/2 cup plain nonfat yogurt; 1/4 cup reduced-fat mayonnaise; ½ lemon, juice only, about 2 Tbsp.; 2 Tbsp. mango chutney or apricot jam; 2 – 3 tsp. curry powder, to taste; 2 celery stalks, large finely diced; 1 cup seedless red grapes, halved; 1/4 cup shelled and unsalted pistachio nuts, or use slivered almonds or coarsely chopped pecans; 12 slices whole wheat bread (optional); 1 head lettuce (optional)