1. In a large non-stick frying pan, heat half the oil over high heat. Cook rump, in two batches, for 2 to 3 minutes or until browned and tender. Set aside on a plate covered with foil.
2. Reduce the heat to medium-high, spray the pan with olive oil and cook the garlic for 30 seconds. Add the stir-fry mix and cook for 3 to 4 minutes, or until vegetables are just tender. Return the beef to the pan, add teriyaki marinade and toss to coat.
3. Meanwhile, prepare soba noodles according to packet instructions. Divide noodles between plates, top with stir fry and sprinkle with green onions, to serve.