Preheat the oven to 350˚F (176˚C) and line a rimmed baking pan with parchment paper.
Drain (reserve the bean juice) and rinse the beans and set aside.
Spread the beans evenly on the parchment lined baking pan and bake for approximately 15 minutes, or until the beans begin to split and some of them have a crispy edge.
In a small pan, toast (stir or shake the pan frequently to avoid scorching) the 1 tbsp chili powder, 1 1/2 tsp cumin, and 1/2 tsp chipotle chili powder on medium-high heat until they release their oils and become fragrant, approximately 2 minutes. Remove from heat.
Grind the 1 1/2 cups oats in a food processor. Use rolled oats only, not steel cut or instant. Make sure they’re certified gluten-free if you are avoiding gluten. Add 1 ½ cups (255 g) of the beans, the 3 tbsp of bean juice, and the toasted spices to the food processor and grind until it forms a solid sticky ball. Approximately 1 minute.
Heat a large cast-iron skillet or a non-stick skillet on medium-high heat and add the 1 tbsp of oil. When the oil is hot, add the chopped onion, peppers, and corn. Cook for approximately 6 to 7 minutes, or until the onion and peppers soften. Stir frequently to avoid scorching. Add the garlic and cook for 2 minutes. Remove from the heat. NOTE: You can use water to cook the vegetables if you don't cook with oil. Start with about 3 tbsp and continue adding by the tablespoon as the water evaporates.
Scrape the bean mixture into a large bowl and add the remaining 1 cup (85 g) of solid beans and the corn and peppers (make sure they’re cool to the touch) and stir to combine. I use my hands to really get in there and make sure that the mixture is completely combined.
Scoop out a heaping 1/3 cup (73 g) of the mixture and roll into a ball, then press into a patty. Repeat with the remaining bean mixture. (You should get between 6 to 8 patties with 1/3 cup (73 g). If you want larger or smaller patties, the amount will vary.) Refrigerate for at least an hour to allow the patties to set. This will help the burgers to stay together during the cooking process.
Once the patties are set, heat a grill or a pan on medium heat. SEE NOTE. Lightly brush both sides of the burgers with vegetable oil. (This will prevent them from sticking to the grill.) Cook for approximately 5 to 7 minutes per side, or until they are lightly browned and heated through. For best results, cover the pan while they're cooking.
Top with grilled onions, shredded lettuce, tomato slices, and guacamole. If you want to skip the bun, wrap it in a lettuce leaf instead of shredding the lettuce, or just eat it with a fork.