Begin by slicing the mushrooms and sautéing them with cooking oil, garlic powder, crushed red pepper, and half of the salt and pepper until their moisture evaporates.
Thaw and squeeze the spinach to remove excess water, aiming for a loosely packed cup.
In a bowl, combine the sautéed mushrooms, spinach, mozzarella, sour cream, and the remaining salt and pepper.
Distribute approximately ½ cup of the filling across one side of each tortilla, then fold to enclose.
Toast the quesadillas in a skillet over medium heat until they achieve a golden-brown crispness outside and melty inside.
