In a large mixing bowl, add turkey, onions, egg, breadcrumbs, garlic powder, parsley, salt and pepper. Use a large spoon (or gloved hands) to mix until combined well.
Form into six 1/3 pound patties or eight 1/4 pound patties. Make sure they are a little larger in circumference than the buns you will be using because they will shrink slightly.
If pan frying, heat a large non-stick skillet to medium-high. Add oil then place patties in the skillet. Cook until browned on one side then flip. Continue cooking until internal temperature reaches 165° F.
If grilling, heat grill to high and cook on both sides until internal temperature reaches 165° F.
Place cooked burgers on buns with toppings of choice.