1To prepare marinade, combine all the ingredients in a shallow dish and mix well.
2Place each chicken breast between 2 sheets of plastic wrap and beat lightly to a uniform thickness of 1.5 to 2 cm. Place in the dish with the marinade, turning to coat well. Refrigerate for 30 mins.
3Heat about 2 cm of oil in a large frying pan over medium heat. Beat the egg whites until fluid and frothy. If water chestnut flour is caked and granular, pound it in a mortar to make it a fine powder, then transfer to a plate or tray. Dip chicken into egg white, then into flour. Fry for 3 to 4 mins or until golden brown and just cooked through. Drain on paper towels.
4To prepare lemon sauce, combine sugar, vinegar, lemon zest, juice and stock in a wok over medium-low heat. Bring to a simmer, stirring to dissolve sugar. Mix the arrowroot with a little cold water and stir into the sauce. Cook, stirring for about 1 min or until the sauce is clear and glossy. Add the carrot and onion; cook for 30 secs to soften.
5Slice the chicken into 2.5-cm strips and arrange over the shredded lettuce. Pour the sauce over the top and serve with rice.
Photo: Bauer/William Meppem