Question: The Double Decker Taco is an offering of which American chain of fast-food restaurants based in Irvine, California?

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Tom Wahl's: Tom Wahl's is a chain of fast-food restaurants based in the Rochester, New York area that currently has several restaurants around the Finger Lakes region.  USA Today named it one of "51 great burger joints across the USA" in 2010.

SBB-CFF-FFS RABe 514: The RABe 514 is a four-car double decker electrical multiple unit used by the Swiss Federal Railways SBB-CFF-FFS for the Zürich S-Bahn.  It is part of the Siemens Desiro Double Deck product family.  The trains are also referred to as DTZ which stands for the German word Doppelstocktriebzug (English: double decker multiple unit).

Kacheguda–Tirupati Double Decker Express: The Kacheguda - Tirupati AC Double Decker Express is a superfast express connecting Hyderabad and Tirupati cities.  It is the first AC Double Decker Express in the states of Telangana and Andhra Pradesh alongside Guntur - Kacheguda AC Double Decker Express.  It has CZDAC coaches (AC chair-car) and VESDA (Very Early Smoke Detection with Alarm system), first of its kind, in a double-decker train.

Chennai - Bangalore Double Decker Express: The Chennai - Bangalore AC Double Decker Express is a superfast express connecting Indian cities Chennai and Bangalore.  It is the first AC Double Decker Express in South India.

Double decker taco: The Double Decker Taco is an offering of Taco Bell restaurants.  It is a traditional crunchy taco with a tortilla secured to the outside with a layer of refried beans.  It is a single item.

Volvo B5TL: The Volvo B5TL is a 2-axle low-floor double decker built by Volvo.  It replaced the B9TL as Volvo's Euro 6 2-axle double decker product for the UK and Irish markets.

Pup 'N' Taco: Pup 'N' Taco (also spelled with a lower case 'n') was a privately owned chain of fast-food restaurants in Southern California; the chain's headquarters were located in Long Beach, California.  The business was begun by Russell Wendell in 1956 as a drive-in restaurant that served tacos, hot dogs, and pastrami sandwiches.  Russell already owned Big DoNut, a chain of successful doughnut stores in Los Angeles that featured gigantic doughnuts atop a drive-in bakery.  The first officially branded Pup 'N' Taco was opened in Pasadena, California in 1965.

Guntur - Kacheguda AC Double Decker Express: The Guntur - Kacheguda AC Double Decker Express was an Superfast Double Decker train belonging to South Central Railway zone that used to run between Guntur Junction and Kacheguda in India.  It was operated with 22117/22118 train numbers on bi-weekly basis.

SJ X40: X40 is a series of electric multiple units operated by SJ of Sweden.  They are in service from Stockholm to Linköping, Eskilstuna/Arboga, Västerås/Örebro and Gävle/Sandviken, and since 2010 to Gothenburg.  The double decker trains are built by Alstom since 2004, with 43 units being delivered, either in a two-car or three-car configuration.  It is based on the Coradia series, very similar to the French SNCF Class Z 26500 double decker trains, and similar to the X60-series.

Taco Bell: Taco Bell is an American chain of fast-food restaurants based in Irvine, California.  A subsidiary of Yum!  Brands, Inc., they serve a variety of Tex-Mex foods, including tacos, burritos, quesadillas, nachos, other specialty items, and a variety of "value menu" items.  Taco Bell serves more than 2 billion customers each year at 7,000 restaurants, more than 80 percent of which are owned and operated by independent franchisees and licensees.

Supporting paragraphs: Double decker taco Taco Bell
Answer: Taco Bell