Cut the cucumber in half lengthwise and then in ¼-inch slices, on the diagonal. Place the cucumber slices in a serving dish, along with the red onion slices.
In a small bowl, combine rice vinegar, fish sauce and agave nectar. Whisk to combine. Add the red chili pepper or dried chile flakes, if using.
Just before serving, toss the cucumber and onion mixture with the dressing. Top the salad with the chopped cilantro and peanuts. Toss well and serve.
Notes
Note 1: Feel free to use more red onion, if you prefer. I find that raw onion tends to overwhelm the other flavors, so I stick to ¼ onion.Note 2: Substitute with honey or sugar, if preferred. If you choose to use granulated sugar, stir the dressing until the sugar dissolves.Note 3: If you're sensitive to spice, leave out the chili pepper/red pepper flakes.Please note that I am not a medical or nutritional professional. I provide nutritional information for my recipes as a courtesy to my readers. It is calculated using the built-in recipe card nutrition calculator. While I attempt to provide information that is as accurate as possible, you should calculate the nutritional information independently before relying on it.