Preheat grill to medium heat.
In the middle of a sheet of foil, place ¼ of the sweet potato slices in a single layer.
On top of that add about ¼ of the sliced onions.
Place a tilapia fillet on top of the onions.
On top of the tilapia, add ¼ of the tomato slices, ¼ of the chopped olives.
Salt and pepper to taste.
Drizzle with one teaspoon of olive oil and sprinkle one tablespoon of chopped parsley over the top.
Pull two sides of the aluminum foil up and fold them over repeatedly to create a seal.
Fold up the two ends of the foil and be sure to seal well.
Repeat with the other three sheets of oil and tilapia.
Place foil packets, seam side up, over indirect heat on the grill.
Grill for about 20 minutes or until tilapia turns opaque and sweet potatoes are tender.