Preparing chicken burgers for sous vide then freezing while keeping shape I am having a hard time finding good, reasonably low fat precooked chicken burgers currently, presumably due to COVID; I used to buy these for reference. As such, I figured I'd prepare my own.
I'm shredding (in a Cuisinart) raw, boneless/skinless chicken thighs (with most of the fat removed that's external but leaving the intramuscular fat), and then adding caramelized onions, cooked garlic/bell peppers, and spices or BBQ sauce, then forming into patties, placing in a vacuum bag, sealing, and cooking in my sous vide at 150 for an hour or so.  Then I let them cool for a bit, and put them in the freezer.  I prepare them from frozen in a pan (directly, no oil or steam beyond what they produce themselves).
Batch one went well, except that they don't keep their shape well.  Between sous-vide and freezer, they end up  in really odd shapes or even bent (presumably because I don't have a perfect spot).
Are there things I can add to the recipe, or to my technique, to help them stay a bit more flat and less thin?  The main thing I've seen that I'm not including is bread/breadcrumbs; I'd prefer to not include that (as it's empty calories), but if this is the specific reason it's in there I could reconsider.  I'm also using thighs, not breasts, in part as they have the fat profile I think is best - but if breast meat would do better in this application, I could certainly switch.
You're missing a binder of some kind. You're adding some fairly moist fillings to ground meat, which is already moist and whose structure has been destroyed. You need something to soak up the juices of your burgers as they cook, and that's the purpose of the breadcrumbs you're missing. I know you said you would prefer not to include them, but that is the easiest and probably best solution. Egg (or just egg white) is another common binder, but with all those already-moist ingredients and no breadcrumbs, I wouldn't recommend it.
However, there are a couple of other options you could try.
You could try adding a few tablespoons of cornstarch or potato starch to your meat mixture. That would have the effect of thickening up juices as they're released during cooking-- if the temperature is high enough for the starches to gel.
Another option is more of a technique (which I confess I've never tried, so I can't personally vouch for its effectiveness). This recipe uses no binders, no breadcrumbs or cornstarch at all. Instead, it calls for a portion of the ground meat to be fried off beforehand and then mixed in with the rest of the ingredients. The mixing in this case is actually kneading; the recipe specifies that kneading very very well is key to maintaining the structure of the finished patty.
In any case, as far as the patties being misshapen from the freezer goes, consider making an attempt to rearrange a flat spot for your burgers, at least when you first freeze them. Once they're solid, they can be moved to a more convenient spot in the freezer.