Preheat the broiler: Preheat oven to broil with a rack about 8 inches from the heat source.
Brown the beef: Heat a large ovenproof skillet over medium-high heat. Add the beef, taco seasoning, and about 1 cup of the onion. Cook, stirring often, until the beef is browned and the onion is translucent, 6 to 7 minutes. Do not drain.
Add salsa and beans: Add the salsa and beans and reduce the heat to medium. Simmer, stirring often, until the sauce thickens and the flavors meld, about 3 minutes.
Build the casserole and broil: Fold in the tortilla chips until just combined. Top with the cheese and transfer to the preheated oven. Broil until the cheese is melted, 2 to 3 minutes. Remove from the oven and top with the lettuce, tomatoes, sour cream, and remaining ¼ cup diced onion. Love the recipe? Leave us stars and a comment below!
