Steam sweet potatoes until soft. Allow to cool, remove skins, and mash in a bowl. Mix in chili pepper, cumin, and salt.
Heat oil in a skillet over medium heat, add onion and garlic, sauté for 3 minutes. Mix in kale, salt to taste, cover skillet, cook for 5 minutes until kale is tender. Add seasoned sweet potatoes and black beans. Set aside.
To prepare the quesadillas, heat a non-stick pan or cast-iron pan over medium heat. Heat each tortilla on both sides until just cooked. Remove the tortillas from the pan, add 3 tablespoons of the sweet potato mixture to half of each tortilla and top with 2 tablespoons of cheese, fold in half. Add a little oil to the hot pan, Fry the tortillas on each side for 2 minutes. Repeat for each tortilla.
Serve warm with yogurt or cream.