1. Parboil sweet potatoes until they're soft and easy to prick with a fork but not mushy. Approx. 15-30 minutes depending on size of potatoes.
2. Put potatoes in cold water to stop cooking. While potatoes cool, mash garlic, red pepper flakes and cilantro into cotija cheese until fully mixed.
3. Cut off ends of potatoes and slice into 1/2 inch rounds. Try to keep skins intact if possible.
4. On a baking sheet sprayed with cooking spray, place largest potato slice down, layer with a couple of onion slices, then cheese. Repeat. Each stack should have three slices of potato, ending with cheese on top. Sprinkle with cumin.
5. Bake for 10-15 minutes at 375 degrees or until cheese browns slightly.
6. Drizzle with olive oil and add more cilantro before serving. Salt to taste.