1. For the chipotle sauce: Combine all ingredients in small bowl; refrigerate until ready to serve. (Sauce can be refrigerated for up to 4 days.)
2. For the burgers: Spread beans onto rimmed baking sheet lined with triple layer of paper towels and let drain for 15 minutes. In large bowl, whisk eggs and flour into uniform paste, then stir in scallions, minced cilantro, garlic, hot sauce, cumin, coriander, and salt.
3. Process tortilla chips in food processor until finely ground, about 30 seconds. Add black beans and pulse until beans are roughly broken down, about 5 pulses. Stir processed bean mixture into egg mixture until well combined. Cover and refrigerate for at least 1 hour or up to 24 hours.
*We added kernels from one ear of fresh corn to the bean mixture
4. Divide bean mixture into 6 equal portions. Using lightly moistened hands, tightly pack each portion into 1/2-inch-thick patty. (Patties can be frozen for up to 1 month. To freeze, transfer patties to parchment paper–lined rimmed baking sheet, cover with plastic wrap, and freeze until firm, about 1 hour. Stack patties separated by parchment paper; wrap in plastic wrap; and place in zipper-lock freezer bag. Thaw patties completely before cooking.)
5. Adjust oven rack to middle position and heat oven to 200 degrees. Set wire rack in rimmed baking sheet. Heat 2 teaspoons oil in 12-inch nonstick skillet over medium heat until shimmering. Place 3 patties in skillet and cook until well browned and crisp on first side, about 5 minutes. Using 2 spatulas, gently flip patties, add 2 teaspoons oil to skillet, and cook until well browned and crisp on second side, 3 to 5 minutes. Transfer burgers to prepared rack and keep warm in oven. Repeat with remaining 4 teaspoons oil and remaining 3 patties. Spread chipotle sauce over bun bottoms. Serve burgers on buns, topped with avocados, pickled onions, and remaining 1 cup cilantro leaves.