Start by rinsing the chicken breasts under cold water. Pat them dry with paper towels, then slice them into bite-sized pieces.
In a bowl, combine the soy sauce, lemon juice, and sugar. Stir until the sugar is dissolved. Add the chicken pieces to the bowl and toss to coat them evenly with the marinade. Allow to marinate for at least 15-20 minutes.
Heat a tablespoon of oil in a non-stick skillet over medium heat. Add the slices of ginger and sauté for about 1-2 minutes until fragrant.
Remove the ginger slices from the skillet and discard them. In the same skillet, add the marinated chicken pieces. Cook for approximately 5-7 minutes, until golden brown and fully cooked through.
Once the chicken is cooked, pour the remaining marinade into the skillet. Let it bubble and reduce for about 2-3 minutes.
Transfer the Chinese Mandarin Chicken to a serving platter and garnish with chopped scallions. Serve hot over rice or noodles.