In a large skillet heat the oil over moderately high heat until hot. Add the scallion, ginger and garlic and cook the mixture, stirring, 30 seconds. Add the chicken and cook the mixture, stirring, until no longer pink. Add the broccoli and cook, stirring, 1 minute more. Add the broth and bring the liquid to a boil, stirring. Simmer, stirring, until lightly thickened. Season with lemon juice and stir in cilantro. Serve over pasta.