In a non-stick skillet over medium heat, add the onion and garlic, sautéing for 5 – 6 minutes, until translucent and aromatic. Add a small splash of water if needed to prevent it from sticking. Incorporate the minced chipotles and adobo sauce, cook for another minute, then remove from the heat.
In a large bowl, mash the black beans well, leaving a bit of texture with some whole beans remaining. Add the sautéed onion and garlic, tomato paste, balsamic vinegar, cumin, sriracha (if using), and black pepper, stirring well to combine. Mix in the oats last, then season with salt to taste.
Line a baking sheet with parchment paper. Create 8 equal patties, each using about a ⅓ cup of black bean mixture. Use a large ice cream scoop or measuring cup for consistency, then gently pat them out with lightly moistened hands. Refrigerate for at least 30 minutes before cooking.
Bake in a 375-degree preheated oven for 20 – 30 minutes, flipping halfway through, until browned around the edges. Serve hot, with your favorite toppings.