In a non-stick skillet over medium-high heat, add the olive oil and ground beef.
Cook the beef while breaking it into small crumbles until browned, approximately 5-7 minutes.
Add the diced onions, chili powder, cumin, and garlic powder to the skillet; sauté for an additional 2-3 minutes until onions are soft.
Season the beef mixture with salt and pepper, then remove from the heat and transfer to a bowl.
Wipe the skillet clean and return to medium heat.
Place one tortilla in the skillet and sprinkle 1/4 cup of cheese over one half of the surface.
Layer half of the cooked beef mixture over the cheese and top with another 1/4 cup of cheese.
Fold the tortilla in half and cook for 2-3 minutes per side until the exterior is golden brown and the cheese has fully melted.
Repeat the process for the second tortilla.
Slice each quesadilla into three wedges and serve with non-fat Greek yogurt as a high-protein alternative to sour cream.