In a large bowl or resealable plastic bag, make a marinade by combining the lime juice, sherry, oil, oregano, and garlic salt. Remove 3 tablespoons of marinade and set aside for the salsa. Add chicken to the remaining marinade, turning to coat. Marinate in the refrigerator for 1 hour.
Remove the chicken from the marinade, and place the marinade in a small saucepan. Heat marinade to boiling, and boil for 1 minute. Place the chicken on a grill with the rack about 8 inches from the heat source. Brush marinade over the chicken. Grill, turning and basting frequently with marinade, about 16 to 20 minutes, or until the chicken is fork-tender. Arrange chicken on a platter. Serve with Salsa, and garnish with avocado slices and tortilla chips.
Combine all ingredients in a bowl, mix together, and chill. Makes 1 cup.