01 - Preheat oven to 400°F. Line a baking sheet with parchment paper.
02 - Arrange diced sweet potato on the baking sheet, drizzle lightly with olive oil, and roast for 20 to 25 minutes until tender. Allow to cool slightly.
03 - In a large bowl, mash roasted sweet potato and black beans together with a fork or potato masher, keeping some texture.
04 - Add chopped red onion, minced garlic, oats, bread crumbs, egg or flax egg, cumin, smoked paprika, chili powder, salt, black pepper, and cilantro if using. Mix thoroughly until uniform.
05 - Divide the batter into four equal parts and shape each into a burger patty.
06 - Heat olive oil in a large skillet over medium heat. Cook patties for 4 to 5 minutes per side until well-browned and heated through. Alternatively, bake on a parchment-lined baking sheet at 400°F for 15 to 18 minutes, turning halfway.
07 - Toast burger buns if desired. Assemble with lettuce, tomato slices, avocado, red onion rings, and desired burger sauce. Serve immediately.