Place the sweet potato rounds on a large baking sheet. You might need two baking sheets if you run out of room. You don't want to overcrowd the sweet potatoes. Toss the sweet potatoes in olive oil and season with salt and pepper. Bake for 20 minutes. Use a spatula to flip the sweet potato rounds. Bake for an additional 10 minutes or until sweet potatoes are crisp.
Remove the pan from the oven and sprinkle cheese and black beans over the sweet potatoes. Bake until cheese is melted, about 5-7 minutes.
Remove pan from oven and top with green onions, cilantro, avocado, and sour cream or Greek yogurt. Serve immediately.