In a medium bowl, combine diced tomato, finely chopped red onion, and fresh spinach. Add in crumbled feta cheese, shredded mozzarella, and dried oregano. Mix thoroughly.

Lay out flour tortillas on a clean surface, and divide the filling mixture evenly among them, placing on one half of each tortilla. Fold the other half over to create a half-moon shape.

Heat a lightly oiled skillet over medium heat. Place the folded quesadillas in the skillet and cook for 3-4 minutes until the bottoms are golden brown.

Gently flip the quesadillas over and cook for an additional 3-4 minutes until golden and crispy.

Once cooked, let the quesadillas rest on a cutting board for 1 minute before slicing them into wedges.

Serve warm with a side of cucumber and tomato salad or tzatziki sauce.