Unfortunately you can't cook while a food truck is moving.

It's not illegal, just difficult (don't ask how I know)

Without the cooking part, Sprig was doing this back in 2014. Delivery staff drives around a neighborhood with a bunch of hot meals.

Sprig only offered 2-3 dishes.

Sprig went out of business.

I don't think that could be made to work for impulse, on-demand ordering ("I've just decided I want food as soon as possible, and my stomach/brain seems to think $dish sounds good"), which in my experience is the bulk of it. People don't plan out what they're going to eat when ordering restaurant food as much, they just do it when they're ready.

At that point you're not a food delivery service, you're a restaurant that only offers delivery.