Put the pork in a bowl with half the stir-fry sauce and toss to coat. Heat the oil in a large frying pan or wok over a medium heat and add the pork. Cook, turning occasionally, for 15 minutes, until cooked through with no pink remaining. Remove from the pan and set aside.
Wipe the pan clean with a piece of kitchen roll. Add the pepper and stir-fry for 1 minute. Stir in the remaining sauce and heat through for 1 minute.
Meanwhile, bring a pan of water to the boil and add the noodles, then cook for 4-5 minutes until tender. Drain and stir through half the spring onions. Divide between 4 plates.
Slice the pork and place on top of the noodles along with the pepper stir-fry. Scatter over the remaining spring onions to serve.