In a medium bowl, mix together pumpkin puree, cumin, garlic powder, and salt until well combined.
Spread about 2 tablespoons of the pumpkin mixture evenly over one side of each tortilla.
Sprinkle the cheese blend over half of each tortilla, then fold the tortilla in half to create a half-moon shape.
Heat 1/2 tablespoon butter in a large skillet over medium heat. Place 2 quesadillas in the pan and cook for 2-3 minutes per side until golden brown and cheese is melted.
Repeat with remaining butter and quesadillas, keeping finished ones warm in a 200°F oven.
Cut each quesadilla into thirds and serve warm with sour cream and salsa if desired.