Heat a non-stick skillet over medium heat and lightly coat with cooking spray or butter.
Place one flour tortilla in the skillet.
Spread the fresh spinach leaves evenly over the tortilla.
Sprinkle the crumbled feta cheese on top of the spinach.
Cover with the second flour tortilla.
Cook until the bottom tortilla is golden brown and the cheese is slightly melted, about 3-4 minutes.
Carefully flip the quesadilla using a spatula, and cook the other side until golden brown, about 2-3 minutes.
Remove from the skillet and let it cool for a minute before cutting into wedges.
Pack in a lunchbox with a side of hummus or tzatziki for dipping.