Put the cucumber, chili pepper, red pepper flakes, ¼ cup of the peanuts, 2 tablespoons of the coconut, lime juice, sugar and 1 teaspoon salt in a large bowl. Toss gently.
Heat the oil in a small skillet over medium-high heat. Add the mustard seeds. When they start to sizzle and pop, stir in the cumin and remaining 2 tablespoons coconut. Turn off the heat.
Pour the mustard seed mixture over the cucumbers and toss everything together (it will sizzle). Taste to make sure the salad has a good balance of salty-sweet-hot adding more salt, sugar, chili or citrus to taste.
Serve in bowls sprinkled with the remaining peanuts and cilantro or mint.