Sauté the onions in the olive oil until they are soft and beginning to brown. Add the spices and garlic and stir until they are fragrant and just beginning to brown and stick to the bottom of the pot. Add the grated sweet potatoes and mix well.
Cover and cook for about 10 minutes, stirring frequently to prevent sticking. (You may need to add a little water with the sweet potatoes if they are sticking.) When the sweet potatoes are tender, add salt and pepper to taste and remove the filling from the heat. Stir in the grated cheese and the cilantro.
Lay a tortilla in a flat pan over medium high heat. Put ½ to ¼ cup filling on half of the tortilla and fold in half.
Cook a few minutes on that side, until the tortilla is crispy, but not burned. Flip to the other side and cook again until that side is crispy as well.
Top with salsa and sour cream if you like.
Adapted from The Moosewood Restaurant Cooks at Home