In a medium bowl, combine the ground beef, onion, Worcestershire, chili powder, oregano, and salt, and mix well. Form into 16 small patties about 1/2 inch thick.
Heat a grill pan over medium heat until hot enough to make a few drops of water sizzle. Put the patties on the hot pan and cook until brown grill marks appear on the bottom, 3 to 4 minutes. Turn over and cook until the meat is no longer pink in the center but still juicy, 2 to 3 minutes, or to the desired degree of doneness. Leave the patties on the pan off the heat.
In a large bowl, combine the lettuce, beans, tomato, avocado, tortilla chips, cilantro and scallions, and toss gently. Add the oil, venegar, lime juice, and 1/4 cup of the salsa. Toss again to mix.
To serve, divide the salad among 4 large plates. Arrange 4 patties on each salad and top each with one-fourth of the cheese. Garnish each salad with a drizzle of sour cream and 1/2 tablespoon of salsa.