Mash half of the black beans in a large bowl. Stir in remaining black beans, quinoa, panko, garlic, minced chipotle, onion powder, and cumin. Once all ingredients are fully incorporated, add salt to taste. Fold in the beaten egg.
Line a baking sheet with parchment paper. Divide the burger mixture into 6 mounds on the baking sheet, then shape each mound into a bun-sized patty. Bake the burgers for about 20 minutes, carefully flipping halfway through baking time. They're done when they're baked through and slightly crispy on the edges. Serve with Sweet Corn relish and your favorite veggie burger toppings.
Sweet Corn Relish
Combine all ingredients in a small saucepan and bring to a boil. Cover and simmer for 10 minutes, stirring occasionally. Refrigerate up to 2 days before serving.
I tested this recipe several times and I preferred ½ tablespoon of chipotle, while Chris preferred a full tablespoon. If you're not sure, I'd start with ½ tablespoon, taste the burger mixture (before you put the egg in!), and add more from there.