Pat the 2 skinless, boneless chicken breasts dry. Heat a skillet over medium-high heat and add oil to coat the pan. When the oil is hot, add the chicken and pan-fry until browned and cooked through, about 5–7 minutes per side (or until an instant-read thermometer registers 165°F / 74°C). Transfer the chicken to a plate and let rest for 3–5 minutes. (If you prefer, you can grill the chicken instead.)

While the chicken is cooking or resting, make the sauce: in a small saucepan combine 4 tablespoons soy sauce, 1 tablespoon lemon juice, 2 tablespoons sugar, and the 3 peeled ginger slices. Heat over medium, stirring occasionally, until the sugar dissolves and the sauce slightly thickens, about 3–5 minutes.

Remove and discard the ginger slices from the sauce.

Slice the rested chicken into pieces. Arrange the sliced chicken on a serving plate, drizzle the sauce over the chicken, and garnish with the chopped scallion. Serve immediately.