Combine first 4 ingredients; refrigerate until ready to prepare sandwiches.
Combine egg whites and next 3 ingredients in a large zip-top plastic bag. Cut chicken breast halves in half horizontally to form 4 cutlets. Add chicken to bag; seal. Marinate in refrigerator for at least 2 hours or up to 8 hours, turning bag occasionally.
Place tortilla chips in a food processor; process 1 minute or until ground. Place ground chips in a shallow dish.
Working with one cutlet at a time, remove chicken from bag, allowing excess marinade to drip off. Coat chicken completely in chips. Set aside. Repeat procedure with remaining chicken and chips.
Heat a large nonstick skillet over medium heat. Add oil to pan, swirling to coat. Add chicken to pan; cook 3 minutes on each side or until browned and done. Spread mayonnaise mixture evenly over cut sides of rolls. Layer bottom half of each roll with 3 onion slices, 1 lettuce leaf, and 1 chicken cutlet; top with top halves of rolls.