In a heavy-bottomed skillet, heat the oil; add the sliced onion,green chili and saute for a minute or so
Add the coarsely mashed boiled sweet potato,mix,add all the remaining ingredients except the cheese
Stir until all of the ingredients are thoroughly blended. Cover the pan, reduce the heat to low, and leave to cook for a few minutes.
Turn off the heat when you're finished. The filling is complete. Set aside.
Place a slice of bread on a flat surface and spoon a little quantity of potato filling on top, spreading it around. Top with shredded cheese.
Then top with the remaining slice of bread. With your palms, press down on the sandwich.
Preheat a skillet or grill pan; spread butter on the top facing slice if desired. Place the sandwich in a hot skillet or grill pan, buttered side down.
Apply butter on the top side, if desired. Press the sandwich down with a spatula to ensure equal grilling and that the filling stays within. Cook until crisp and gently browned on the opposite side.
Note: You can grill your spiced potato sandwich in a sandwich maker and serve it for breakfast or pack it in a school lunch box if you want.
To make a balanced breakfast, serve the cheese and sweet potato sandwich with a smoothie.