Preheat oven to 350F. Line a small baking sheet with parchment paper and spread beans out in a single layer. Bake beans at 350F 10-12 minutes until just slightly dried out. Allow to cool.
Heat 1 tablespoon oil in a small skillet over medium-high heat. Add onion and pepper and sauté 3-4 minutes until tender. Add garlic and cook 1 additional minute until fragrant.
Scrape vegetables into a fine-mesh sieve and gently press on vegetables to drain out liquid. Set aside.
Place beans in a large bowl and use a fork to gently mash to a paste (you will want several chunks) Add vegetables, chipotle, chili powder, cumin, breadcrumbs, egg, and salt and pepper to taste. Gently fold black bean mixture until just combined.
Form black bean mixture into 4 patties. Wrap well and refrigerate until ready to use (patties may be refrigerated up to 6 days and frozen up to 1 month)
Heat 1 tablespoon vegetable oil in a large nonstick skillet over medium-high heat. Working in batches, add burgers and sear 3-5 minutes on each side, flipping once until burgers are golden brown and heated through. Repeat cooking with remaining patties, adding more oil to pan as needed.
Serve burgers on toasted buns with buttermilk slaw spooned on top. Serve immediately and enjoy!