Place the raw chicken breasts in a pot and cover with water. Bring to a boil, then reduce heat slightly and simmer for 10-15 minutes, or until the chicken is fully cooked.

Transfer the chicken to a bowl and let it cool. Once cool, shred the chicken using two forks.

In the bowl, combine the shredded chicken with Greek yogurt, Dijon mustard, celery, and a pinch of salt and pepper.

Stuff the sub roll with the chicken salad, top with lettuce (or other low-calorie toppings) and serve.

Meal Prep Note: Store the filling separately from the rolls and assemble just before eating to keep the bread from getting soggy.