Add a little bit of oil to the largest non-stick pan you have and heat to medium-low.
Put the spinach in the pan and stir until it has softened.
Take the spinach out of the pan and increase the heat to medium.
Add a tortilla to the pan and add in ¼ of the cheese to half of the tortilla. Top with half of the spinach and sliced green onions and diced tomatoes then cover with another ¼ of the cheese.
Fold the tortilla over to make the quesadilla.
If you have room in the pan, add the other tortilla and build the quesadilla the same way, otherwise cook them one at a time.
Allow the quesadillas to cook on one side about 2 minutes before flipping. The bottom of the tortilla should be crisp and have browned and the cheese should be melting.
Cook for another minute or two on the other side before serving.
Serve with your favourite salsa, sour cream, or gaucamole.