Pre heat oven to 375 degrees. Place diced sweet potatoes and diced onion on a baking sheet, drizzle with olive oil and sprinkle with taco seasoning. Roast for 15-20 minutes in oven or until tender. Place 3 tortillas on a baking sheet evenly divide sweet potato-onion mixture and top with shredded cheese. Top with remaining 3 tortillas, brush top of tortillas with olive oil and place in oven. Bake until cheese melts, about 3-5 minutes. Serve warm, sliced.