In a medium bowl, mash the black beans with a fork until mostly smooth but still containing some texture.
Whisk the egg in a separate small bowl, then add it to the beans along with nutritional yeast, hemp seeds, garlic powder, onion powder, sea salt, and black pepper.
Mix the ingredients thoroughly and let the mixture sit for 5 minutes to allow the nutritional yeast and hemp seeds to absorb moisture.
Heat the olive oil in a non-stick skillet over medium heat.
Form the bean mixture into two thick patties and place them in the skillet.
Cook for 4-5 minutes per side until the patties are firm and golden brown.
While the burgers cook, whisk the Greek yogurt and lime juice together in a small bowl to create the sauce.
Place each patty onto a butter lettuce leaf, top with sliced avocado, and drizzle with the yogurt sauce.