Last year's top performing restaurant stock was not Chipotle Mexican Grill (NYSE:CMG) or Buffalo Wild Wings (NASDAQ:BWLD). It was Fiesta Restaurant Group (NASDAQ:FRGI). I wrote about Fiesta Restaurant Group back in December after shares ran up more than 240% for the year. Last year, both Chipotle Mexican Grill and Buffalo Wild Wings delivered gains of slightly less than 100% for their shareholders.

Source: Fiesta Restaurant Group

This year is turning out to be a different story for Fiesta Restaurant Group, the owner of Pollo Tropical, Taco Cabana, and Cabana Grill. Shares of Fiesta Restaurant Group are down almost 20% year to date. On the other hand, Chipotle Mexican Grill shares have risen more than 11%, and shares of Buffalo Wild Wings are higher by more than 3% year to date. For investors, is this just profit taking in shares of Fiesta Restaurant Group, or is there another reason shares are weak this year?

A closer look at first-quarter results
While Fiesta Restaurant Group reported growth for the first quarter, I think the market was looking for a little bit more from the company. Total revenue increased only 8.8%, while same-store sales increased 6.3% at Pollo Tropical and only 0.8% at Taco Cabana. I think the market expected double-digit growth from the company, much like how Chipotle Mexican Grill is delivering. In Chipotle's first quarter, its same-store sales rose an impressive 13.4%.

Source: Pollo Tropical

The two bright spots were earnings growth and restaurant expansion. Earnings per share grew more than 60% from $0.20 last year to $0.33 this year. Fiesta Restaurant Group was able to boost its profits by implementing modest price increases and improving its supply chain. As a result, its cost of sales decreased as a percentage of total restaurant sales.

Source: Taco Cabana

The highlight of the quarter, in my opinion, was the fact that the company finally decided to expand its concepts into other markets. Pollo Tropical has most of its locations in Florida, while Taco Cabana is based in Texas. In the first quarter, Pollo Tropical opened its first Texas location outside of Dallas. This location is the first of 10 locations that are expected to open in Texas this year. Besides Pollo Tropical expanding, Cabana Grill opened its first location in Atlanta.

Fiesta Restaurant Group's outlook remains bright
This year, Fiesta Restaurant Group plans to open a total of 22 to 26 new company-owned restaurants. Already, Fiesta Restaurant Group has 16 locations under construction. The overall strategy is to go west with Pollo Tropical and east with Taco Cabana.

Source: Cabana Grill

In terms of Cabana Grill, the plan is to hopefully have a third concept that the company can grow. The Atlanta location is its first location, and the company will be opening a second location in Jacksonville, Fla. later this year. Cabana Grill is an improvement upon the Taco Cabana concept, with additional menu items and the hope of appealing to a broader audience. On the company's earnings call, CEO Tim Travis said, "[I]f our Cabana Grill concept performs as planned, it represents another potential growth vehicle for our company."

Chipotle continues to outperform
Chipotle Mexican Grill shares are higher by almost 20% in the past month alone. The restaurant chain has been implementing a series of price hikes on its menu without any major backlash from its customers. Overall, the prices for core menu items increased 6.5%, while side items and drinks increased an average of 7.3%. These price hikes will help boost Chipotle's top and bottom lines, which the market is liking. Earnings and margins should continue improving throughout the year.

Source: Chipotle Mexican Grill

Buffalo Wild Wings is looking pretty good as well
Buffalo Wild Wings shares are higher by almost 9% in the past month. In the first quarter, Buffalo Wild Wings saw same-store sales rise 6.6% at its company-owned stores and 5.1% at its franchised locations. Earnings per share came in $0.14 better than analysts' estimates, and revenue grew more than 20% year over year. One of the prime reasons for the strong results was that Buffalo Wild Wings benefited from lower chicken wing costs. In the first quarter, chicken wing prices were 35% lower than last year.

Source: Buffalo Wild Wings

Foolish final thoughts
I think the prime reason that shares of Fiesta Restaurant Group are lower this year is because of profit taking. Investors are locking in profits from the big gains last year. However, for shares of Fiesta Restaurant Group to continue higher, the company will have to deliver the fast growth investors have come to expect from high-flying restaurant chains. Shares are not what I would call cheap, as they trade at nearly 28 times next year's earnings. For now, I think investors are better off on the sidelines and waiting until after Fiesta Restaurant Group reports its second- quarter earnings.