Pat the chicken breasts dry and season both sides with salt and black pepper.
Heat 2 teaspoons sesame oil in a large nonstick skillet over medium-high heat.
Add the chicken to the hot skillet and cook until golden brown on both sides and nearly cooked through, about 4–6 minutes per side depending on thickness.
Drain the mandarin oranges into a bowl and reserve 1/4 cup of the syrup; add the drained oranges and the reserved 1/4 cup syrup to the skillet and simmer for 2 minutes.
In a small bowl, whisk together 1/2 cup fat-free chicken broth, 1 tablespoon low-sodium soy sauce, and 2 teaspoons cornstarch until smooth.
Pour the broth mixture into the skillet with the chicken and oranges and simmer, stirring occasionally, until the sauce thickens and the chicken is cooked through, about 3 minutes.
Remove from heat, slice or shred the chicken if desired, and serve topped with chopped green onion and rice if using.