Preheat oven to 400 degrees. Lightly grease a baking sheet with olive oil. Cut the sweet potato in half lengthwise and place facedown on the pan. Bake for about 30 minutes, until fork tender and cooked through. Remove from oven. Lower the oven to 375 degrees.
When the sweet potatoes are cool enough to handle, peel off the skin and add the flesh to a large bowl. Mash with a potato masher, add the black beans and slightly mash the beans into the sweet potatoes, leaving some beans whole.
To the bowl with the sweet potatoes and black beans, add the diced red onion, oats, cumin, smoked paprika, onion powder, garlic powder and 1/2 teaspoon salt. Stir well with a large spoon until combined. Taste, add more salt if desired.
Prepare a baking sheet for the burgers by either lightly greasing with oil or using parchment paper. You can use the same pan you cooked the sweet potato on.
Fill a 1/2 cup measuring cup, then form into a burger shape, about 1 inch thick. You can make them thinner or thicker as you prefer. Place burgers on the prepared baking sheet. Bake for 15 minutes, flip carefully and bake for 15 more minutes. Remove from oven.
Optional Sriracha mayo: In a small bowl, stir together the vegan mayo (homemade or store bought), Sriracha and a tiny pinch of garlic powder.
Serve in buns with optional Sriracha mayo (or regular vegan mayo), lettuce, tomato slices, red onion and/or avocado slices.