Chipotle Mexican Grill announced the return of its annual Halloween celebration, Boorito on October 31 from 3 p.m. to closing at all Chipotle locations. Customers dressed in costume will score $3 burritos, bowls, salads or tacos. Boorito fans can go all-out with complex costumes that took weeks to make or simply show up in an over-sized t-shirt carrying a couple of frozen waffles (stranger things have happened).

“Boorito is a tradition that we started in 2000, to simply give a treat to our customers while celebrating Halloween. It’s gotten to the point that for our long-term customers, we don’t even need to mention Boorito anymore, as they’re coming in anyway knowing they’re going to have a great time enjoying the food they love, all while supporting a good cause,” says Mark Crumpacker, chief creative and development officer at Chipotle.

What started as just a fun way to celebrate Halloween has turned into a very effective fundraiser. Over the last four years, through Boorito Chipotle customers have helped raise $4 million for the Chipotle Cultivate Foundation simply by coming in dressed in costume. Proceeds from this year’s event, up to $1 million, will benefit the foundation established in 2011 to allow Chipotle to extend its commitment to creating a more sustainable food future.

This is one event that really does put the “fun” in “fundraiser”—where Chipotle customers can have good fun and good food, for a good cause.