Add spinach, salt, black pepper, and nutmeg to a 12-inch sauté pan over medium heat. Cover and cook until the spinach has wilted, about 3 to 5 minutes. Allow the spinach to cool for a few minutes.

Place the spinach in a fine mesh strainer to remove excess moisture. Chop the spinach.

Distribute half of the mozzarella cheese over one half of each tortilla.

Distribute chopped spinach over top of the mozzarella cheese. Sprinkle crushed red pepper flakes and oregano over the spinach.

Top the spinach with the remaining mozzarella cheese, feta, and garlic powder. Fold each tortilla to form a half-moon shape.

Heat 1 tablespoon of olive oil in a large non-stick frying pan over medium-low heat. Cook two quesadillas at a time, adding more oil between batches.

Cook quesadillas for about 3 to 4 minutes on one side, then flip and cook for another 3 to 4 minutes until golden brown and crispy.

Cut each quesadilla in half to serve as 8 pieces. Serve with plain Greek yogurt, if desired.