In a large bowl, toss the chopped spinach, feta, mozzarella, sun-dried tomatoes, olives, oregano, and garlic powder until well combined.
Lay each tortilla flat and distribute the spinach and cheese mixture evenly over one half of each tortilla.
Fold the tortillas in half to enclose the filling.
Heat 1/2 tablespoon of olive oil in a large non-stick skillet over medium heat.
Place one quesadilla in the skillet and cook for 2 to 3 minutes per side until the tortilla is golden brown and the cheese has melted.
Repeat the cooking process for the remaining quesadillas, adding oil as needed.
Slice into wedges and serve immediately.