Simmer chicken in a pot of water over medium heat to an internal temperature of 160°F. Remove from water. Dice chicken into small bitesized pieces and refrigerate to cool fully.
Once cooled, thoroughly mix the chicken, onion, pecans, cranberries, and mayo, in a bowl. Season with salt and pepper to taste.
Lightly toast the bread.
Layer the bread with spring mix, chicken salad, and cheese. Cut in half and serve with pickles.
Notes
Pro tip: Cut the chicken breasts into similar sized chunks to cook faster. (If the chicken is diced or cut too small prior to simmering in water it has the potential to dry out or overcook).