In a medium saucepan, heat 1/2 inch of vegetable oil over moderately high heat until a deep-fry thermometer registers 350°. Add the tortillas and fry, stirring occasionally, until crisp and lightly golden, about 1 1/2 minutes. Using a slotted spoon, transfer the tortillas to paper towels to drain; season with salt.
In a medium soup pot, heat 2 tablespoons of the oil used to fry the tortillas. Add the onion and cook over moderate heat until softened, about 6 minutes. Add the cumin and cook for 1 minute. Add the beans and their liquid and 1 1/2 cups of water. Bring to a simmer and cook until slightly thickened, about 15 minutes. Stir in 1 tablespoon of the cilantro and season with salt and pepper. Ladle the soup into bowls and top with a few tortillas. Sprinkle with the remaining 1 tablespoon of cilantro and serve.