Whisk together broth, soy sauce, lemon juice and cornstarch in a bowl; set aside.
Warm oil in a wok or large skillet over medium-high heat until hot. Add beef, turn heat to high and cook, stirring constantly, until no longer pink, 2 to 3 minutes.
Add broccoli and cook, stirring, until warmed through, about 2 minutes.
Stir in reserved sauce, orange zest and juice. Cook, stirring constantly, until sauce is thickened, about 2 minutes. Season with salt and pepper.