1. Combine chicken breast halves and water to cover in a medium saucepan; cover and bring to a boil. Reduce heat and simmer 20 minutes or until chicken is done; drain well. Remove chicken from bone; coarsely chop chicken.
2. Place coarsely chopped chicken in a 1 quart casserole dish coated with vegetable cooking spray and sprinkle with salt and pepper. Combine cream of chicken soup, skim milk and yogurt in a medium bowl, stirring until well blended; pour soup mixture evenly over chicken.
3. Combine crushed crackers and melted butter, stirring until well combined. Sprinkle cracker mixture evenly over top of casserole. Bake at 350 degrees for 20 minutes or until thoroughly heated.
