Cut the cucumber in half lengthwise, then repeat with each half until you have a number of long strips. Now slice the other way to dice the cucumber, then place in a large salad bowl.
Add the shallot, green onion, chili/red pepper, and cilantro to the cucumber. Keep back a few cilantro leaves to garnish the salad.
Combine the dressing ingredients (fish sauce to sugar), stirring to dissolve the shrimp paste. (I didn't have shrimp paste so just added a bit extra fish sauce).
The dressing will taste pungent now, but will be perfect once it's on the salad!
Pour dressing over salad and toss well.
Top with the ground/chopped peanuts and extra cilantro.
If serving this salad as a main course, add 1 cup cooked baby shrimp as a protein source.
Serve immediately, or cover and refrigerate for up to 3 hours. Note that the longer this salad sits, the more liquid will gather at the bottom of the bowl (some of this is cucumber juice, some is dressing!) If making ahead of time, just make sure to re-toss.