1. Combine stock, oyster sauce, cornstarch and sesame oil in a bowl and set aside.
2. Cook soba noodles according to package directions. Drain and set aside.
3. In large nonstick skillet or wok, heat 1 tsp of oil over medium-high heat. Cook chicken untill lightly golden, about 3 minutes. Transfer to plate.
4. Add remaining oil, beans, mushrooms, garlic, chilli and ginger to pan; cook, stirring, until fragrant, about 1 minute. Add capsicum and bok choy. Cook until tender but crisp, about 4 minutes.
5. Add sauce mix , noodles and chicken to pan; cook, stirring to coat with sauce, for 1 minute.