In a large skillet over medium heat, add the ground beef. Cook until browned, breaking it up with a spatula, for about 5 minutes.
Add the diced onion and minced garlic to the skillet. Cook until the onion is translucent, about 3 minutes.
Stir in the chili powder, cumin, salt, and black pepper. Cook for another 2 minutes until everything is well combined. Remove from heat.
Lay out four tortillas on a clean surface. Divide the beef mixture evenly among the tortillas, leaving space at the edges.
Sprinkle the shredded cheddar and mozzarella cheese over the beef mixture on each tortilla.
Top with the remaining tortillas to create quesadilla sandwiches.
Heat 1 tablespoon of vegetable oil in the skillet over medium heat. Place two quesadillas in the skillet and cook for about 3-4 minutes on each side until golden brown and the cheese is melted.
Once cooked, remove from the skillet and cut each quesadilla into wedges. Serve warm with optional toppings.