Cook the beef in a large saucepan over medium-high heat, breaking it up with a spoon, until browned, 5 to 6 minutes. Spoon off and discard any excess fat. Add the onion and garlic and cook, stirring occasionally, until tender, 5 to 6 minutes. Add the chili powder, flour, cumin and 1/4 teaspoon pepper and cook, stirring, for 1 minute.
Add the tomatoes (and their juices), tomato sauce, beef broth and Tabasco and simmer until the mixture has thickened, 15 to 20 minutes. Add the beans and chiles to the skillet and simmer for 5 minutes.
Meanwhile, heat the broiler. Transfer the meat mixture to a 2-quart broiler-proof baking dish. Top with the corn chips and sprinkle with the scallions and cheese. Broil until the cheese melts and is beginning to brown, 3 to 4 minutes.