Heat 1/2 tablespoon of olive oil in a non-stick skillet over medium heat.
Add red onions and sauté for 2 minutes until translucent.
Add fresh spinach to the skillet and cook until fully wilted; drain any excess liquid to prevent sogginess.
Wipe the skillet and add the remaining 1/2 tablespoon of olive oil over medium-low heat.
Place one tortilla in the skillet and distribute half of the mozzarella cheese evenly.
Layer the sautéed spinach, red onion, sun-dried tomatoes, feta cheese, and oregano over the mozzarella.
Top with the remaining mozzarella and the second tortilla.
Press down firmly with a spatula and cook for 3 to 4 minutes per side until the tortillas are crisp and golden.
Transfer to a cutting board, let rest for 60 seconds, and slice into 4 wedges.