Make the chicken salad: Fill a medium saucepan with water and bring to a boil. Meanwhile, season chicken with salt and pepper. When water boils, reduce heat, add chicken, and simmer until cooked through, 8 to 10 minutes. Remove and let cool. Cut into 1/2-inch pieces. In a bowl, combine yogurt, mustard, chives, apricots, and almonds. Stir in chicken and season with salt and pepper.
Top one slice toast with lettuce and 1/2 the chicken salad mixture. Top with second slice.