Fatburger To Floyd Mayweather -- Don't Leave Us Champ ... We Made A Skinny Burger For You!!

Floyd Mayweather can now eat guilt-free at his favorite guilty pleasure ... 'cause a Las Vegas Fatburger just concocted a brand new training-friendly organic burger ... just for the champ.

TMZ Sports broke the story ... Floyd is so serious about beating Pacquiao on May 2 that he's adopted an all-organic diet during training ... courtesy of a $1,000-a-plate chef.

We spoke to the chef, who told us the real bummer of the new diet was saying goodbye to the 3 AM Fatburger visits that Floyd lives and dies for.

Well, it turns out Fatburger isn't about to take losing the (big tipping) champ lying down ... wielding their culinary wizardry to create an all-organic beef experience that Mayweather can scarf while he trains.

Darin Feinstein owns the Vegas Fatburger Floyd chomps at and he tells us he was so serious about the burger that he outsourced the creation of it to his other restaurant, the totally organic El Dorado Cantina.

"The meat is from the Sunfed ranch, highest quality beef. The lettuce, tomato, onion, relish, even the special sauce is all organic."

Feinstein says all it takes is one call from Floyd and the burger can be made at El Dorado and delivered to Fatburger so Money can pick it up and grub.

Meantime, Pacquiao's eating chocolate ...