Heat oil in a large skillet over medium-high heat until it shimmers. Add chopped onion and cook until it softens slightly, about 5 minutes. Add tortilla chips. Add eggs to the pan and stir around with the chips until almost set, 3 to 4 minutes. Pour in black beans and salsa. Stir to combine and heat through, about 5 minutes.
Top chilaquiles with queso fresco, red onion, avocado, and cilantro. Serve immediately.