Warm a non-stick skillet over medium heat and add a splash of olive oil.
Add the chopped spinach to the skillet and cook for about 2 minutes until wilted, stirring occasionally. Remove from pan and set aside.
Lay a tortilla flat on a cutting board and spoon a quarter of the cooked spinach evenly over half of it.
Sprinkle crumbled feta over the spinach, distributing it evenly for maximum flavor in every bite.
Fold the tortilla in half, pressing gently to help the filling settle inside.
Carefully place the folded tortilla into the preheated skillet and cook for about 2-3 minutes until the bottom is golden brown and crispy.
Flip the quesadilla with a spatula and cook the other side for another 2-3 minutes until golden and the cheese begins to melt.
Remove the quesadilla from the skillet and let it rest for a minute to settle.
Slice the quesadilla into wedges and serve immediately, or let it cool for a quick, portable snack.