Peel the squash with a potato peeler. Chop off the stalk and flower end. Chop in half and use a spoon to remove the seeds. Chop into 1 cm cubes.
Heat the sesame oil in a wok (or a large pan, if you don't have a wok). Put the squash in the wok and cover. Cook for 5 minutes.
Peel the onion and slice it finely. Add it to the wok and cook for 2 minutes, stirring regularly.
Break the cauliflower into small florets and add to the wok. Cook for 3 mins, stirring regularly.
Slice the runner beans into 1 cm chunks and add to the wok. Cook for 2 minutes, covered.
When all the vegetables are almost cooked, mix together the sauce: the sweet chilli sauce, and the peanut butter. If the sauce is thick, add a little water, if you find it hard to mix. Add to the wok and stir well.