Heat olive oil in a skillet over medium heat. Add diced onion and garlic, sauté until fragrant.
Add ground beef to the skillet, breaking it apart with a spatula. Cook until browned.
Stir in chili powder, paprika, salt, and pepper. Mix well and remove from heat.
Lay a tortilla flat and sprinkle cheese on one half. Add a scoop of beef mixture, then top with more cheese.
Fold tortilla in half. Repeat with remaining tortillas.
Melt butter in a large skillet. Cook each quesadilla until golden brown on both sides and cheese has melted.
Cut into wedges and serve warm with sour cream, salsa, or guacamole.