Heat oven to 200C/180C fan/gas 6. Mix together the soy, ketchup and honey with the five-spice. Put the pork tenderloin on a baking tray and brush with just under half the sauce. Roast in the oven for 10 mins, then brush with a little extra sauce and return to the oven for a further 15 mins.
Meanwhile, soak the noodles in boiling water until soft. Drain, reserving about 50ml of the water. Heat the sesame oil in a wok or large frying pan, add the corn and sugar snap peas, and stir-fry for 3 mins, adding the water to help the veg steam.
Add the stir-fry veg and half the spring onions, and cook for 3 mins more until wilted. Tip in the noodles and the rest of the sauce. Using tongs, mix everything to combine. Remove the pork, cut into slices and serve on top of the noodles. Scatter with remaining spring onions.