Stir together quinoa and 1½ cups water in small saucepan, and season with salt, if desired. Bring to boil. Cover, reduce heat to medium-low, and simmer 20 minutes, or until all liquid is absorbed. (Makes 1½ cups cooked quinoa.)
Meanwhile, place onion and tomatoes in medium nonstick skillet, and cook over medium heat. (Oil left on tomatoes should be enough to sauté onion.) Cook 3 to 4 minutes or until onion has softened.
Stir in ½ cup black beans, garlic, blackening seasoning and 1½ cups water. Simmer 9 to 11 minutes or until most of liquid has evaporated.
Transfer bean-onion mixture to food processor, add ¾ cup cooked quinoa, and process until smooth. Transfer to bowl and stir in remaining ¾ cup quinoa. Season with salt and pepper, if desired, and cool.
Preheat Indoor/Outdoor Grill on setting 4. Shape bean mixture into 8 patties (½ cup each), and place on grill. Grill for about 8 to 10 minutes or 4 to 5 minutes per side.
Serve on pretzel rolls with your standard burger condiments.
