Prep all ingredients: chop onion, drain beans and corn, measure out spices.
Cook ground beef and onion in a skillet over medium heat for 5-7 minutes until browned.
Drain excess fat, then stir in black beans, corn, diced tomatoes, and taco seasoning. Cook for an additional 3-4 minutes.
Assemble the casserole in a greased baking dish, layering meat mixture, sour cream, cheese, and tortilla chips.
Bake in a preheated oven at 350°F for 25-30 minutes until cheese is melted and bubbly.
Let cool for 5 minutes, then garnish with sliced green onions before serving.