Sweet Potato Quesadillas

1 1/2 cups finely chopped onion
2 garlic cloves, minced or pressed
3 tablespoons vegetable oil
4 cups grated peeled sweet potato (about 3 potatoes)
1/2 teaspoon dried oregano
1 teaspoon chili powder
2 teaspoons ground cumin
generous pinch of cayenne
salt and ground black pepper to taste
1 cup grated sharp cheddar cheese

8 tortillas (8- to 10-inch)
commercial Mexican-style tomato salsa
sour cream
Saute the onions and garlic in the vegetable oil until the onions are translucent. Add the grated sweet potatoes, oregano, chili powder, cumin, and cayenne and cook, covered, for about 10 minutes, stirring frequently to prevent sticking. When the sweet potato is tender, add salt and pepper to taste and remove the filling from the heat. Spread one-eighth of the filling and 2 tablespoons of the cheese on each tortilla.
Serve immediately, topped with salsa and sour cream.