Preheat oven to 350 degrees Fahrenheit.

Heat olive oil in a large skillet over medium heat.

Add chopped onion and minced garlic to the skillet and sauté until translucent.

Add lean ground beef to the skillet and cook until browned, breaking it apart with a spoon.

Drain any excess grease from the skillet.

Stir in Mexican-style tomatoes, taco seasoning mix, diced green chilies, and sliced black olives into the skillet.

Simmer the mixture for about 10 minutes, stirring occasionally.

Grease a 9x13 inch baking pan to prevent sticking.

Layer half of the crushed tortilla chips over the bottom of the prepared baking pan.

Add all of the meat mixture evenly over the layer of chips.

Sprinkle the shredded mozzarella cheese over the meat mixture.

Spread the sour cream evenly over the mozzarella cheese.

Top with the remaining crushed tortilla chips.

Bake in the preheated oven until heated through, about 30 minutes.

Sprinkle the shredded cheddar cheese over the top of the casserole.

Continue baking until the cheddar cheese is melted and bubbly.

Let the casserole stand for 5 minutes before serving to allow it to set.