The fast-casual segment -- and the restaurant industry as a whole -- has been in a major slump over the past year. Lower grocery prices are leading more people to choose to eat at home rather than dine out, and many restaurants are struggling with declining traffic and lost sales.

Yet as JAB Holding Company's recent $7.5 billion acquisition of Panera Bread Company demonstrates, there's still value to be had in the fast-casual space. Moreover, the recent downturn has made valuations much more attractive for some of the best fast-causal businesses, thereby creating a buying opportunity for astute investors. In this regard, read on to learn about what is perhaps the biggest bargain among fast-casual stocks available in the market today.

Chipotle Mexican Grill burritos

Image source: Chipotle Mexican Grill.

It's been a rough stretch for Chipotle Mexican Grill (NYSE:CMG) over the past couple of years. The fast-casual burrito chain's stock price is down nearly 60% from the highs it hit back in 2015, as it struggles to overcome the aftermath of multiple food-safety incidents.

Wall Street firms are downgrading its stock. Analysts are questioning whether Chipotle, in its weakened state, can withstand an onslaught of new competition. And even some of my Foolish colleagues are concerned about the fragility of Chipotle's brand following its recent foodborne illness problems.

Therein lies our opportunity.

It's true that the recent norovirus outbreak at one of Chipotle's Virginia restaurants came at exactly the wrong time, as the burrito chain is still recovering from its previous incidents. But this occurrence was related to a single employee making the mistake of working while sick. It was not a food-supply issue like the E. coli crisis that sickened hundreds of people in 2015. That's not to say this latest incident should be dismissed out of hand, but it also doesn't point to a systemic failure of Chipotle's recent food-safety improvements. Unfortunately, norovirus occurrences at restaurants are more common than many people realize.

Thus, while the norovirus incident will no doubt be another setback for Chipotle, it's unlikely to derail its long-term recovery. In its most recent quarter, the company's same-store sales rallied 8.1%, and that's following a 17.8% rise in the first quarter. Comps may be temporarily dented by recent events, but it's doubtful that they will plunge, or even that growth will stall for long.

What has plunged, however, is Chipotle's stock price. Shares are now trading near $315, down sharply from the all-time high of $758 they reached in August 2015. The bears would argue that even at these levels, Chipotle's stock trades at 67 times trailing  earnings and 41 times analysts estimates for 2017. But that's based on Chipotle's current low level of profitability following its food-safety incidents. Its forward P/E falls to 29 times analysts estimates for 2018,  and less than 21 times the $15.10 in EPS that Chipotle earned in 2015.

Moreover, Chipotle now operates over 300 additional restaurants and has reduced its share count by roughly 7% through stock buybacks since that time. So if Chipotle's sales and margins can recover to even close to the levels it achieved prior to its food-safety incidents, it could surpass that $15 EPS figure -- and perhaps sooner than many investors currently expect. In this scenario, investors who purchase Chipotle's shares today would be paying roughly 20 times earnings for a business that has typically commanded a P/E multiple of more than 40. As such, Chipotle's current stock price could prove to be quite a bargain for long-term investors, who are willing to remain patient as the fast-casual chain works toward restoring its lost revenue and profits, and is eventually rewarded for it by the market.

Joe Tenebruso has no position in any of the stocks mentioned. The Motley Fool owns shares of and recommends Chipotle Mexican Grill. The Motley Fool has a disclosure policy.