Place the TVP and vegetable broth together in a large bowl. Stir to combine and let sit for 20 minutes.
When the chickpeas are room temperature, place 1 1/2 cups of them into a food processor with the S blade in place. Pulse the chickpeas a few times until partially puréed, but still chunky. Reserve the remaining whole chickpeas in the fridge for another cooking project or snack.
Place the TVP vegetable broth mixture in the food processor with the chickpeas. Add the breadcrumbs and flax seed. Season the chickpea TVP mixture with the liquid smoke, chili powder, cayenne, and salt and pepper to taste.
Shape into the chickpea mixture into 6 evenly sized patties with your hands. Place in the refrigerator for at least 2 hours or in the freezer for 20 minutes. Take the burgers out of the fridge 30 minutes before grilling to allow them to come back to room temperature.
Preheat the grill to medium-high heat.
Place the chickpea burgers on the grill and cook for 7-8 minutes per side, or until they are cooked to preference. Place the buns on the grill to toast to preference, if desired. Place each chickpea burger on a bottom half of each toasted bun, top with a few slices on the onion and avocado, close the burgers with the top buns, and enjoy!