Preheat oven to 450.
Place poblano peppers on a baking sheet and lightly brush with olive oil. Roast peppers for 15 minutes, flip, then cook another 10 minutes or until blackened on both sides.
Transfer peppers to a bowl and cover with plastic wrap.
After about 10 minutes (or when cool enough to handle), remove skin, seeds, and stems from peppers, then chop them.
While the peppers are cooking, combine barley, 1 cup water, and 1/4 tsp. salt in a small pot on high heat.
Bring water to a boil, then reduce heat to low, cover, and cook barley until tender (about 35 to 40 minutes).
Meanwhile, heat 2 tsp. olive oil in a medium pan over medium-high heat. Add carrots and onion. Season with salt, then cook until lightly browned and tender, stirring often.
Add garlic, chili powder, cumin, and oregano to veggies; cook until fragrant, about 30 seconds, stirring constantly. Remove from heat.
Blot excess liquid from black beans with a paper towel, then place in a large bowl. Mash until about 3/4 smooth.
Add barley, sauteed veggies, walnuts, cilantro, green onion, chipotle pepper, and adobo sauce. Mix well, then season to taste with salt.
Stir flour and egg into bean mixture until well combined.
Heat remaining 2 tsp. olive oil in a large pan over medium heat.
Shape bean mixture into 4 patties (or 6 patties for smaller burgers), then add to pan.
Cook burgers until browned on one side, then flip. Top with cheese and cook until burgers are browned on other side.
Serve burgers on buns with tomato and lettuce. Enjoy!