Heat olive oil in a large skillet over medium heat. Add bell pepper, celery, mushrooms, onion, garlic, pine nuts, cumin, paprika, salt, pepper and cayenne and cook, stirring frequently, until softened, about 5 minutes.
Put beans in a large bowl and mash well with a fork. Add maple syrup, panko crumbs, egg, and rice. Mix in the sautéed vegetables and stir to combine. Form into 6 patties.
Heat 1 tablespoon olive oil in a large skillet over medium heat. Arrange patties in a single layer (working in batches, if needed) and cook, flipping once, until golden brown on both sides and cooked through, about 10 minutes. Grill the buns and place a patty on each bun, top with your favorite toppings.