Position a rack in the center of the oven and pre-heat the oven to 400°F.
Line a baking sheet with parchment paper.
Prepare a sheet of foil paper by folding it to hold the bloc of feta cheese. Place the cheese on the foil and set aside.
Peel and cut sweet potatoes into wedges.
In a large bowl, toss the sweet potatoes wedges with olive oil, dried oregano, chilli flakes, sumac, salt and pepper.
Spread sweet potatoes in a single layer onto baking sheet and bake in the oven for approximately 20 minutes.
After 20 minutes, turn the sweet potatoes and add the feta cheese (in the foil container) onto the baking tray. Bake for an additional 10 to 12 minutes until potatoes are tender and nicely browned and the feta cheese has softened.
Remove the baked Feta cheese from the tray place it in a small bowl and add the yogurt and oregano. Mix well. Serve cheese mixture on the side or top the sweet potatoes with it.
These sweet potatoes wedges are on the spicy side, if you prefer your food less spicy, reduce the amount of chilli flakes or omit entirely.