Preheat oven to 375F.
Combine olive oil, melted butter or non-dairy spread, garlic, spices, salt and pepper and half the cilantro in a small mixing bowl; stir to combine.
Spread 1-2 tablespoons of the mixture in the bottom of a 9 x 13 inch baking dish.
Arrange sweet potato slices in the dish and brush potatoes with the remaining olive oil mixture, reserving a couple of teaspoonfuls.
Cover with foil and bake for 45 minutes.
Remove foil and increase oven temperature to 450F.
Roast potatoes for an additional 15 minutes, or until potatoes are slightly browned. Allow an extra 5 to 10 minutes at high altitude or if your sweet potatoes are large.
Remove sweet potatoes from the oven and test an end piece for doneness. If the sweet potatoes have dried out during roasting, brush them with reserved seasoned olive oil.
Garnish with cilantro leaves.