This zuǒ reading is only a classifier for a tuft of hair or grass, as in 一撮头发 (a tuft of hair). For a pinch of powder or the verb 'to gather', the character is read cuō.
Left hand radical, the side form of 手. It indexes 撮 in the action-with-hands family: 抓 (grab), 捏 (pinch), 摘 (pluck). It names the pinching gesture of gathering a tiny amount between thumb and fingertips.
Right side 最 supplies the sound, zuì drifting to cuō. Faintly semantic too: 最 originally meant 'to gather all together', and 撮 means to gather a tiny pinch by hand.
