Heat the olive oil in a large skillet over medium heat. Add the onion and cook until softened, about 5 minutes. Add the ground beef and cook until browned, about 10 minutes. Drain off any excess fat.
Stir in the garlic powder, cumin, chili powder, salt and pepper. Cook for 1 minute.
Lay out two of the tortillas on a work surface. Divide half of the beef mixture between them and spread it out evenly. Sprinkle with 1 cup of cheese on each.
Place the remaining two tortillas on top of each quesadilla. Press down lightly.
Heat a large skillet over medium heat. Place one quesadilla in the skillet and cook for 3-4 minutes per side or until golden brown and cheese is melted.