Bring a pan of salted water to the boil. Add the sugar snaps, boil for 2 minutes, then scoop into a colander with a slotted spoon and refresh under cold water. Slice lengthways and leave to drain on kitchen paper. Add the asparagus and broad beans to the boiling water and cook for 2 minutes. Drain, refresh and drain again on more kitchen paper. Pop the broad beans out of their skins.
Break the lettuces into separate leaves; tear any larger leaves, then scatter them in a bowl or on a large serving platter. Next, scatter over the sugar snaps, asparagus spears, broad beans and thinly sliced cucumber.
Put all the ingredients for the dressing into a food processor and blend until smooth. Add a tablespoon of cold water to make a drizzle consistency. Season to taste.
Drizzle the dressing over the salad, sprinkle with the toasted pumpkin seeds and chopped chives, and serve straight away.