Cut up the onion, garlic (if not using pre-minced), and tomatoes.

Heat 1 tablespoon olive oil in a large skillet over medium heat for one minute, then add the diced onion and saute for two minutes. Gradually stir in half of the spinach.

Saute spinach over medium heat until dark green and wilted, stirring occasionally.

Meanwhile, shred the mozzarella.

Once your first round of spinach is done, place it in a strainer. Add 1 tablespoon olive oil to the same large skillet, then add in the garlic and saute just briefly.

Gradually stir in the second half of the spinach. Saute the rest of your spinach over medium heat until dark green and wilted, stirring occasionally.

Add the the rest of the cooked spinach to the strainer. Drain the spinach, squeezing out as much excess water as possible with the back of a large spoon.

Move the cooked spinach into a bowl, then stir in the feta crumbles, oregano, and crushed red pepper.

Wipe out the skillet and add just a bit more olive oil. Heat the oil over medium heat for one minute, then start cooking the quesadillas.

Assemble your quesadillas three at a time: Top half of each tortilla with shredded mozzarella, some of cooked spinach & feta mixture, and halved grape tomatoes. Fold each tortilla over its filling.

Brown the quesadillas three at a time over medium heat for about a minute a side, or until they are nicely browned and the cheese has melted.

Repeat this process until you have used up all of the tortillas and filling.

Serve your spinach feta quesadillas with sour cream, or other desired fixings.