In a medium bowl, combine diced large tomato, finely chopped red onion, and fresh spinach. Add crumbled feta and shredded mozzarella cheese along with dried oregano. Gently toss together until well mixed.

Ensure the spinach is moisture-free to prevent sogginess. Squeeze out excess water from the fresh spinach if necessary.

On a clean, flat surface, lay out three flour tortillas. Evenly distribute a generous amount of filling on one half of each tortilla.

Carefully fold each tortilla over the filling, pressing gently to secure the edges.

Heat a skillet over medium heat for about two minutes. Lightly oil the skillet surface.

Place the folded quesadillas into the hot skillet and cook for about 3-4 minutes until the bottom is golden brown and crispy. Flip each quesadilla and cook the other side for an additional 3-4 minutes.

Once fully cooked, remove from skillet and rest on a cutting board for about one minute.

Using a sharp knife, cut each quesadilla into halves or triangular pieces and serve warm.