Heat oil in 12-inch nonstick skillet over medium heat until shimmering.
Add tortilla strips and fry until spotty brown, about 7 minutes; transfer to paper towel–lined plate.
Cook beef, onion, and salt in now-empty skillet over medium-high heat, breaking up meat with spoon, until browned, about 6 minutes.
Reduce heat to medium and stir in enchilada sauce and 2 cups tortilla strips.
Simmer until slightly thickened, about 5 minutes.
Sprinkle remaining 1 cup tortilla strips, Colby Jack, olives, and scallions over top.
Reduce heat to low and cook until cheese is melted, about 3 minutes.
Serve with sour cream.
