Preheat oven to 375ºF degrees. Line a baking tray with parchment paper. Place sweet potatoes on the tray and bake until fork tender, about 25 to 30 minutes. Remove from oven and set aside to cool. When cool, scoop out flesh into a bowl. This can be done a day or two in advance and stored in the fridge.
Place black beans in a large mixing bowl. Using a fork or the back of a wooden spoon, lightly mash the beans. Add sweet potato flesh, almond meal, oat flour (or bread crumbs), jalapeño, garlic, scallions, lime juice, cumin, chili powder, chipotle powder and salt. Taste and adjust seasonings. Let mixture sit for about 5 minutes.
Use the same tray and parchment paper from sweet potatoes and drizzle with olive oil. Scoop out bean mixture using a 1/4 cup measuring cup or portion scoop onto the tray, leaving about 2 inches in between. Use a knife or small spatula to flatten into patties that are 3-4 inches wide and about 3/4 inch thick. Bake at 375ºF for about 35 minutes. Remove tray from oven and let set for about 5 minutes. They may be too fragile to move if you don’t allow for the setting time. Serve on buns or simply on lettuce, with sliced avocado, tomato, and cashew sour cream. Extra black bean cakes can be stored in a container with parchment paper in between layers in the fridge or freezer.