I do think the burger looks plenty yummy, just the sort I wouldn't mind queuing for.
For a commercial presentation/promotional photograph, I think the burger needs some modeling/posing help.
First the bun:
Choose one with a much more uniform top half, one that doesn't look like it has been sat on.
The lettuce:
The fold on camera left is all wrong. If it is going to be folded because that's how the burger is prepared, rotate the lettuce so the fold is out of sight to the back side of the burger, present crisp leafy edges to the camera.
The tomato:
Lovingly sliced for uniform thickness, posed to show both the skin and a bit of the deep red and succulent fruit flesh within, include some seeds is possible.
The sauce:
Ugh, the worst part of the photo. Get the sauce trail out of the shadows, into the light, a broader trail, I think probably a bit off center, or a lot off center as you see fit. A viewer of the photo should get a sense of the color(s), texture(s) and viscosity of the sauce.
The burger:
What the heck is that dime sized dark spot on camera left? If it's a feature, show it well enough to define it, if it's a flaw, shoot a different burger.
If they are hand forming the patties, have them form one that is 'just so' with a mind to its visual presentation.
I see on your flickr that it's a stuffed bacon and cheese burger.
The cheese oozing out of the patty is clearly obvious in your photo, the bacon less so.
The fries:
Of course fries will be served up in random positions. Your photo of the fries should appear random as well but in reality, each fry should be placed 'just so' for maximum visual benefit.
The fries look to be skin on, show the skin to best effect, a few should also be broken, perhaps steaming.
Camera to subject angle:
Camera appears to have been about at table level, I think that's all wrong. I think it would be an odd sight indeed for someone to have their chin on the table looking at their meal before eating.
Raise the camera for a more normal/natural perspective.
This looks like the sort of meal served in a basket. If so, and if a wicker type basket is used, the meal could be presented in the basket, again, just so, or the basket could be used as a framing element behind or to one side.
If one of those common red plastic baskets is used, use one maybe as an out of focus background stop.
Whatever that out of focus background is, don't be lazy and just throw a large aperture at it, crop it out in the finder during composition, raising the camera for a downward view may be all that's needed, might just happen naturally if you follow the camera to subject angle suggestion above.
Lighting:
The light looks to be coming mostly from the right at your three o'clock. I think maybe stepping to your right to where the light is closer to 12:45 ~ 1:30 might show the burger better while still retaining some shadow drama.
Others more experienced than I have already posted some lighting suggestions above, whatever you do, take control. Available light does not have to be totally restrictive. You have the option of moving both the subject and the camera's viewpoint relative to the light source.
Does the Grateful Grill serve beverages? Perhaps there's a drink in a photogenic bottle that can be included as an element?
Anything attractive about their napkins? If paper, probably not. If cloth, even plain cloth, an artfully folded napkin, even a partial view, could be another desirable element.
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Here's a couple years old youtube from McDonald's Canada.
https://www.youtube.com/watch?v=oSd0keSj2W8
While I certainly feel they've compromised whatever corporate moral integrity they might have displayed in falsely presenting a pig's ear as a gilt lined silk purse, several of their composition and presentation techniques could be applied with honesty and integrity.
