1. Cut steak diagonally across the grain into thin strips. Sprinkle with salt and pepper.
2. Stir-fry steak, in 2 batches, in 1 Tbsp. hot oil in a large cast-iron or stainless-steel skillet over high heat 2 to 3 minutes or until meat is no longer pink. Transfer to a plate, and wipe skillet clean.
3. Whisk together beef broth and next 4 ingredients in a small bowl until smooth.
4. Stir-fry Brussels sprouts in remaining 1 Tbsp. hot oil over high heat 2 minutes or until lightly browned. Add jalapeño pepper, ginger, and garlic, and stir-fry 1 minute. Pour soy sauce mixture over Brussels sprouts, and bring mixture to a boil. Cook, stirring often, 3 to 4 minutes or until sprouts are tender. Stir in mint and steak. Serve over rice.