Preheat the oven to 375°F (190°C).
Heat olive oil in a large skillet over medium heat. Add diced onion and cook until softened, about 3-4 minutes.
Add minced garlic and cook for 1 minute until fragrant.
Add ground beef to the skillet. Cook, breaking it apart with a spoon, until browned and cooked through, about 6-8 minutes. Drain excess fat if necessary.
Stir in the taco seasoning mix, black beans, corn, salsa, and tomato sauce. Mix well and cook for an additional 5 minutes, allowing flavors to combine. Season with salt and pepper to taste.
In a large mixing bowl, combine the cooked beef mixture with half of the shredded cheddar and Monterey Jack cheeses. Stir to combine.
Lightly grease a 9×13 inch casserole dish. Spread half of the tortilla strips evenly on the bottom of the dish.
Pour half of the beef mixture over the tortilla strips and spread evenly.
Add another layer of the remaining tortilla strips followed by the remaining beef mixture, spreading evenly.
Top the casserole with the remaining shredded cheddar and Monterey Jack cheeses.
Bake uncovered in the preheated oven for 20 minutes, or until the cheese is melted and bubbly.
Remove the casserole from the oven and let it cool for 5 minutes.
Spread sour cream evenly over the top.
Garnish with sliced black olives, chopped green onions, and chopped fresh cilantro before serving.