The company's expansion plans and use of digital channels are delivering impressive business performance.Shares of restaurant chain Chipotle Mexican Grill (CMG 0.07%) have gone on an incredible run over the past few months. The stock was at a 52-week low of $1,768.64 last October, and since then, zoomed up to a high of $3,260 on May 10.Adding to the fervor around shares is the company's March 19 announcement of a 50-for-1 stock split, one of the biggest in the history of the New York Stock Exchange. Shares ...