To make the beans, heat the oil in a sauce pan and saute the onions for about 5 minutes or until translucent, add the garlic and cook for 2 minutes more.
Add the beans, water, ground cumin, salt and pepper. Cook for about 10 minutes, stirring often with a wooden spoon.
Mash the beans using a potato masher and stir well. Set aside.
In a large bowl, add the ground beef, garlic, scallions, onion, cumin, salt and pepper. Mix well and refrigerate for about 1 hour. Form 4 patties.
Heat a grill or sauté pan and cook the hamburgers for 5 minutes on each side until done. Remove to a plate and cover with aluminum foil.
Serve burgers with lettuce, guacamole, tomatoes, red onions, refried beans and queso fresco.