Let the sweet potatoes cool and cut them in half vertically. Scoop out the flesh into a bowl.
Mix the spices with oil and brush the chicken breast. Heat a griddle pan or put the oven on to grill setting. Cook on each side for about 5-5 minutes. Let it rest for a 5 minutes then cut in into bite-sized chunks.
Add the chicken to the sweet potatoes together with the spring onions and minced garlic. Season to taste, and add a couple of pinches of chilli flakes. Mix well.
Fill the sweet potato skins with the filling and scatter some cheese on top, if used.
Bake in the oven for about 10 minutes until warmed through and the cheese has melted.
Serve warm.