Heat olive oil in a large skillet over medium heat. Add the chopped spinach and red onion, sautéing for about 2-3 minutes until the onion is translucent.
In a mixing bowl, combine the cooked spinach mixture, cherry tomatoes, feta cheese, black olives, oregano, garlic powder, salt, and pepper. Mix well to combine.
Place one tortilla in the skillet and spread half of the filling mixture evenly over one half of the tortilla. Fold the other half over the filling. Cook for about 3-4 minutes until the bottom is golden brown.
Carefully flip the quesadilla and cook for another 3-4 minutes until the other side is golden brown and the cheese is melted.
Remove from the skillet and let it cool for a minute before cutting into wedges. Garnish with fresh parsley before serving.
Repeat the process with the second tortilla and remaining filling.