**Prepare the filling**
In a mixing bowl, combine chopped spinach, crumbled feta cheese, garlic powder, and black pepper. Mix well to evenly distribute the flavors.
**Assemble the quesadillas**
Lay a tortilla flat and spread a portion of the spinach and feta mixture over half of it. Fold the tortilla in half to create a semicircle. Repeat with the remaining tortillas and filling.
**Cook the quesadillas**
Heat a large skillet or griddle over medium heat and add a drizzle of olive oil or a small pat of butter. Place a folded tortilla in the skillet and cook for 2–3 minutes on each side, or until golden brown and crispy. Repeat with the remaining quesadillas.
**Slice and serve**
Transfer the cooked quesadillas to a cutting board and slice into wedges. Serve warm with your favorite dips or toppings.