More firm veggie burgers

1:3 ratio of Chia seeds to water. Let it gel up like egg consistency. Great egg replacement. I also ground up some oats into flour. Freeze the patties and then cook them after.

I like to make black bean burgers with lots of onion and garlic, roughly following a Mark Bittman recipe (it relies on oatmeal and egg as a binder) -- but they still do tend to fall apart. I freeze them in parchment, then brush them with oil, still frozen, and bake them. I wouldn't trust them on a grill.

There area few tactics that improve their holding-together-ness. Forming smaller patties, cooking a bit cooler and longer and only flipping after well and truly done all seem to help. And finally, the last batch I made was way, way too big, and I stored a few dozen in the freezer for over six months. I've noticed that the burgers have actually improved -- my guess is that freezing them dehydrates them just a bit, so they aren't so wet and floppy.

Still, if I were grilling I'd go for a pile of portabella mushroom caps, a somewhat passé food that I still adore!

I haven't tried this in veggie burgers. But I use unflavored gelatin (1/2 tsp to 1 cup stock) in turkey and chicken burgers. It keeps them moist.
There are other veggie based products for gelling...you could try experimenting with those mixed with the veggie stock...chilling the burger before cooking, so they firm up.
I don't do that for turkey burger as it's mostly to give it more moisture.

Or you could just try freezing them before grilling.
It would make an interesting cooking experiment to try it with veggie burgers.

Something else that works is ground flax seed - wonderful thickener and good for you.

I get an email newsletter from VegNews magazine, and they just sent this recipe. I think that using TVP and Panko (or bread crumbs) makes this firm enough for the grill.
http://vegnews.com/articles/page.do?pageId=4318&catId=11
Another approach is to get a screen or basket that is used for cooking vegetables, that would keep your burgers on top of the grill, not in it. (And you could adapt using TVP and/or bread crumbs to make a firmer patty.
And if you have a really good burger, post the recipe!

What is your ingredient list? This is a very common problem and I'd like to meet the person who comes up with a grill-ready vegetarian patty. I do like to make mine in a hot cast iron pan with some oil, allowing them to really solidify before flipping. As for the mush factor: adding nuts, seeds, small chunks of veggies will give them some more texture.

For a different idea: if you just want to grill a vegetarian-friendly item, I'd really recommend marinated firm tofu (about 1/2-inch think slabs, pressed dry then soaked in a nice flavorful marinade for a few hours...grilled over medium flame). Again, don't THINK About touching these to flip them until they're really browned and chewy on the bottom. The best grilled tofu I've had, texture-wise, was when I left it for long because I got distracted.