Heat 1 tablespoon olive oil in a skillet over medium heat. Stir in onion; cook and stir until onion is softened, about 5 minutes. Set aside to cool.
Place butternut squash in a large bowl, and season with curry powder, cumin, sea salt, and black pepper. Toss with a fork, then stir in the egg, garbanzo-fava bean flour, and corn flour. Mix in cooled onions.
Heat 2 tablespoons olive oil in a skillet over medium heat. Scoop about 1/4 cup of the butternut squash mixture into the pan. Flatten to a patty about 1/4-inch thick. Pan fry until crisp and browned, about 3 minutes per side. Repeat with remaining squash mixture.
Top with sour cream and pumpkin seeds before serving.