Success in one key area could dramatically improve the stock's long-term growth prospects.Chipotle Mexican Grill (CMG 0.40%) has unwrapped its most serious challenge since the health outbreaks of the previous decade. The stock of the Newport Beach, California-based company is down more than 35% since peaking in December of last year, and with sales growth decelerating rapidly, investors seem less tolerant of its elevated valuation.This leaves prospective shareholders in a predicament. Should they stay away ...