Preheat oven to 425°F (220°C).
In a large pan, sauté mushrooms and red onion until golden brown and most of the moisture has evaporated.
In a food processor, pulse almonds into a coarse meal.
Add cooked rice, sautéed mushrooms and onions, flaxseed, breadcrumbs, BBQ sauce, liquid smoke (if using), smoked paprika, garlic powder, salt, and pepper to the food processor. Pulse until well combined but still retaining some texture.
Form mixture into 4 patties and place on a parchment-lined baking sheet.
Bake for 25-30 minutes, flipping halfway through, until crispy on the outside and firm to the touch.
Toast the sourdough buns.
Assemble your burgers with the baked patties, sliced avocado, watercress, tomato, red onion, vegan mayo or hummus, and extra BBQ sauce.