Preheat oven to 350 degrees. Prep a medium casserole dish with cooking spray. Set aside.
In a large skillet over medium heat, saute vegetable oil and onions until soft, approximately 4 minutes.
Add ground beef, crumbling as you go. Cook and turn until fully browned. Drain meat and onion and return to pan.
Add beef broth, drained diced tomatoes, cilantro and taco seasoning. Toss to coat and heat, approximately 3 minutes.
Add sour cream and 1/2 cup shredded cheese. Mix and then remove from heat to allow mixture to thicken.
Roughly crumble half of the tortilla chips with your hands, place in the bottom of the casserole dish. Top with half of the browned beef mixture and then half of the remaining shredded cheese. Repeat these layers once more.
Place in oven, uncovered, for 20 minutes.
Remove and allow to cool for 5 minutes before cutting to serve and topping with desired toppings.
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