Preheat oven to 350 degrees F (175 degrees C). Lightly grease a large casserole dish.
In a skillet over medium heat, sauté onions until almost translucent. Stir in beef, garlic, and chili peppers, and continue cooking until the meat is no longer pink. Pour in the tomato sauce and chili powder. Mix thoroughly and heat through. Remove from heat.
Spoon a little of the meat mixture into a corn tortilla and add small amounts of salsa, Cheddar cheese and olives. Fold the tortilla up and place in the prepared casserole dish. Repeat for the remaining tortillas using up all of the meat mixture. Reserve 1/4 cup of Cheddar cheese for topping.
Pour the other half of the tomato sauce and sour cream over all of the tortillas. Top with green onions and 1/4 cup of reserved Cheddar cheese.
Bake 30 minutes in the preheated oven, or until hot and bubbly.
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