In a medium saucepan, heat oil over medium low heat. Stir in flour until blended and light brown in color. Slowly pour in broth and whisk to make smooth gravy. Add chili powder, cumin, and garlic powder. Bring to boil and reduce heat to low and simmer for 8-10 minutes. Remove from heat and cool slightly. Pour gravy into a medium size bowl in which to dip tortillas.
Brown ground beef in large skillet. Drain excess fat. Add one package of taco seasoning and tomato sauce and stir to combine. Bring to boil and then reduce heat to low and simmer 8-10 minutes. Remove from heat and set aside until ready to assemble layers.
Spray bottom of 9 x 13 baking dish with non stick spray. Dip two tortillas into gravy and place into baking dish. Cover with one fourth of ground beef, cheese and onion. Repeat 3 times.