Prepare the cucumber: Trim the ends off the cucumber and cut it in half lengthways. Scoop out the seeds with a teaspoon, then use a vegetable peeler to cut each half into long, thin ribbons. Place them in a salad bowl.
Add the greens: Thinly julienne the spring onions and add them to the cucumber. Shred the baby gem lettuce lengthways into long thin strips and toss everything together.
Make the dressing: Put the hoisin sauce, grated ginger, soy sauce, rice vinegar, sesame oil and 2 tablespoons of cold water into a bowl. Mix well, then taste and adjust the seasoning. The water loosens the hoisin so it coats the ribbons evenly rather than clumping.
Dress and serve: Pour the dressing over the salad and toss gently. Serve straight away alongside duck pancakes, grilled chicken or any Asian-style main.
