The musician, who is the son of actors Will Smith and Jada Pinkett Smith, brought the 'I Love You' eatery to the Skid Row area of the city, which has one of the largest homeless populations in America.
'Free vegan food'
Jaden shared the news about the truck on Instagram, posting a photo and writing: "I Love You Restaurant is a movement that is all about giving people what they deserve - healthy, vegan food for free.
"Today, we launched our first one-day food truck pop-up in Downtown LA. Keep a lookout because this is the first one of many."
An Instagram video of the food truck shows bags of food being handed to waiting diners. Each back says: "I love you."
Jaden Smith has won praise for the philanthropic gesture from multiple people, including his parents, who re-shared his images on social media.
His father Will Smith wrote: "Now THAT is the way to Celebrate your Bday!! I love U, Diggy."