I made the spinach and fava bean veggie burgers and found them underwhelming. The original recipe had an egg. I left that out and subbed a couple tablespoons of almond butter to act as a binder. Even after refrigerating, the burgers didn't hold up well in the pan, soaked up a ton of oil while frying, and then had a mushy texture that felt more fritter-y than burger-y to me. Maybe there's a better egg sub than the almond butter, but I doubt I'll make these again.
If you ever change your mind, I recommend ground flax seeds blended with water in a blender until it forms a mixture as viscous as egg. Use 1 part flax seeds to 3 parts water. I think 1/4 cup of the blended mix (1 Tbsp. flax seeds and 3 Tbsp. water) is equivalent to one egg.