1. In a small bowl, combine soy sauce, lemon juice, cornstarch, dark brown sugar, garlic and pepper. set aside.
2. Heat 1 tablespoon vegetable oil in a large skillet or wok over medium-high heat. Add beef and stir-fry until almost cooked through, about 2 minutes. Transfer beef to a plate and cover to keep warm.
3. Heat remaining oil in skillet. Add onion and stir-fry for 5 minutes. Cut broccoli into florets and add to skillet with 1/2 cup water. Bring to a boil. Cover, reduce heat and simmer for 3 minutes.
4. Return beef to skillet with soy sauce mixture. Add ginger. Bring to a boil and cook, stirring constantly, until sauce thickens. Serve hot.
