Chunks of blue cheese add a rich flavor to this lunchtime classic. Slideshow: More Chicken Sandwich Recipes
In a large pot cover the chicken breasts with water. Bring to a gentle simmer and cook for 15 to 20 minutes, or until cooked through. Remove the chicken from the water and let cool. Cut into 1/2-inch pieces and set aside.
In a large bowl combine the mayonnaise, mustard and chili powder. Stir in the chicken, red onion and blue cheese. Season with salt and pepper, to taste.
Spread chicken salad over 4 slices of bread, top with desired toppings and cover with remaining slices of bread.