1. In a food processor, pulse the pecans with the cornstarch, thyme, paprika, 1 1/4 teaspoons of the salt and 1/8 teaspoon cayenne until the nuts are chopped fine. Transfer the mixture to a medium bowl.
2. Whisk together the egg and the water in a small bowl. Dip each chicken breast into the egg mixture and then into the nut mixture.
3. In a large nonstick frying pan, heat the oil over moderate heat. Add the chicken to the pan and cook for 5 minutes. Turn and continue cooking until the chicken is golden brown and cooked through, 5 to 6 minutes longer.
4. Meanwhile, in a small bowl, combine the mayonnaise, mustard, vinegar, sugar, parsley, a pinch of cayenne and the remaining 1/4 teaspoon salt. Serve the chicken with the mustard dipping sauce.