Prepare Simply Salsa™ Mix as directed on package. Chill 1-2 hours. Place chicken breasts in slow cooker, sprinkle with Fiesta Party Dip Mix™; spoon 1/2 cup prepared Simply Salsa™ Mix over chicken. Cook on low for 4-6 hours or until chicken is done. Pull apart and shred chicken breasts; serve with taco shells and toppings. Makes 6-9 servings.