In a deep skillet, combine soy sauce, sugar, lemon slices, garlic, and grated ginger. Bring this mixture to a boil over medium heat, stirring to dissolve the sugar completely.

Add the diced chicken to the boiling sauce. Cook the chicken, stirring regularly for approximately 10 minutes, or until the chicken is cooked through and no longer pink.

In a small bowl, mix the cornstarch and water until smooth. Pour this mixture into the skillet with the chicken and sauce, stirring well. Continue cooking for an additional 3 to 5 minutes until the sauce thickens to your desired consistency.

Remove the lemon slices from the skillet. Serve the chicken immediately over rice or noodles. Top with sliced green onions and sesame seeds, if desired, for added flavor and presentation.