To make the sweet-sour sauce, combine hot water and mustard in a small bowl. Add apricot preserves; mix well and set aside.
To prepare the sesame chicken nuggets, combine the egg white, ginger, garlic, and salt in a shallow bowl or pie plate; mix well. Dip chicken pieces in egg mixture; shake off excess. Coat lightly with sesame seeds, pressing gently to slightly flatten chicken. Heat oil in a large skillet over medium-high heat. Add chicken and cook until golden brown and cooked through, about 3 minutes per side. Serve with sauce.