Place chicken pieces between 2 sheets of plastic wrap and pound lightly with flat side of a mallet until about l/4 inch thick. Combine marinade ingredients in a bowl. Add chicken and stir to coat. Let stand for 10 minutes. Combine sauce ingredients in a saucepan; set aside. Combine salsa ingredients in a bowl; set aside.
Place a frying pan over medium heat until hot. Add 2 tablespoons oil, swirling to coat sides. Dredge chicken in cornstarch; shake to remove excess. Dip into egg, drain briefly, and then coat with panko. Pan-fry chicken, turning once, and cook until golden brown, about 3 minutes on each side. Remove and drain on paper towels.
Heat sauce over medium heat and cook, stirring, until sauce boils and thickens.
To serve, cut chicken into bite-size pieces, arrange on a plate, and pour sauce over the top. Serve with salsa on the side.